Even in these supposedly liberal times, reference to transvestism provokes hilarity or mockery. Men who wear women's clothes are seen as indulging in a clandestine, minority activity, and largely written off as a rather unsavoury group of sexual deviants. My own involvement in their world was initially prompted by an interest in the significance of clothes. As an anthropologist specialising in material culture - my department at the time was the Pitt Rivers Museum in Oxford which overflows with a wondrous range of cultural artefacts - I was astonished to find that although such aspects of material culture as basket-weaving and ceramics had been intensely examined by anthropologists, remarkably little attention had been paid to clothes, in particular to dress, as a marker, a way of announcing distinctions. This seemed an odd omission. Clothing is, after all, one of the most elaborate codes we possess: it is an extraordinarily potent signifier, replete with symbolic meanings. And it is also pretty well ever-present. You may not walk down the street every day bearing your distinctive coloured pot or your carefully woven basket, but you are unlikely to appear in public unclothed.

Probably the simplest distinction that can be found in the complex language of clothes is that between male and female clothing. Almost everywhere in the world - except perhaps in enforced sartorial regimes like Maoist China - clothing is, to a greater or less degree, gender-differentiated. Modern industrialised societies like our own may have eclectic and often ambiguous dress codes, but differentiation is still evident. It somehow seems crucial to us as human beings that visual clues mark out who is male and who is female. There are, of course, certain 'biological' reasons for this distinction being marked. We don't want to court the wrong sex. But this does nothing to explain the different degrees of distaste and opprobrium which are attracted by those who choose to wear clothes belonging to the opposite sex. It is now, for example, perfectly possible for women in the UK to wear just about every item of traditional male dress without raising a single eyebrow. The situation is utterly different for men who choose to wear female garments. In a culture which at least aspires towards some sort of sexual egalitarianism, in which there is an openness about sexual debate, and much talk among feminists and others about the importance of breaking down essentialist notions of gender, why is it that male transvestism should attract so much hostility and ridicule?

Transvestism has, of course, nothing to do with Lily Savage or the characters portrayed in Priscilla, Queen of the Desert. They are drag queens, not regular, habitual, cross-dressers. Transvestism is, however, the issue in Just Like A Woman and Tootsie, where the aim of the cross-dresser is not the provision of a flamboyant eye-catching display of women's clothing, but the far more modest wish of a man to persuade the outside world that he is female. Drag is essentially a performance activity which often parodies women. It is, like the cross-dressing in pantomime, carried on with full audience approval. Both performer and audience acknowledge the 'real sex' underneath. In transvestism, men wish not just to pass as women but to participate in a women's world, in women's behaviour and activities. They wish to show their capacity to display women's sensibilities, to be as much like a woman as possible.

In the UK the main organisation for transvestites is the Beaumont Society, which proved wonderfully helpful to me in the course of my research. They answered my lengthy questionnaire in their droves, I went to their social evenings, their houses, their meetings in pubs - and they came to visit me. One of the transvestites I interviewed was a man in his forties from the north of England called Shelly. His first memory of wanting to cross-dress went right back to the age of four when he begged Father Christmas to bring him a cowgirl outfit (he did not oblige). From that time on he cross-dressed regularly so that he could be on the same wavelength as a woman, so that he could be in touch with their way of thinking. "We dress to please our minds, not our bodies," he told me. Shelly has never enjoyed the company of men and finds their conversation - both their way of speaking ("hard, impersonal, less caring") and their chosen topics (cars, football, drinking) extremely alien.

Although much of the time he dreams of having been born a woman, he would not consider gender re-assignment. "Surgery," he maintained, "removes the maleness but cannot really make you into a woman - just further from being a man." Being a transvestite, he argues, is much like being born with an ability to sing or draw. It is something which simply cannot be removed.

Like many transvestites, Shelly says that he is fully heterosexual. He cross-dresses for the 'feeling' of being a woman and in order to assume the emotions and behaviours associated with femaleness, not for any erotic reasons or compulsions. For transvestites the delight comes from having successfully passed into a different country, into the world of the feminine, and not from any sort of sexual thrill.

My interviews with transvestites revealed how much time they spent thinking about what is for most of us the relatively taken-for-granted activity of getting dressed. They wondered if they would be able to 'pass' in this or that garment, if they dared to adopt it in public, if they could carry off a conversation or an encounter as a woman. Often they expressed resentment against a supposedly modern and egalitarian society which could not allow them to escape from what they say is the specific range of emotional expression associated with their gender. They could not understand why they should be pilloried for wanting to display perceived feminine qualities of passivity, gentleness and softness, for wanting to cross the gender boundary.

Their predicament must lead us to ask whether or not the binary view of gender which prevails in the West is regarded as similarly obvious elsewhere. All the evidence suggests that it is not. Geographic and historical research reveals an extraordinary number of culturally approved ways of crossing gender. In India I spent some time studying the hijras, a defined group of men who live as women. They may have been born with indeterminate genitalia; more usually they have had their genitals removed (in something more akin to a religious ceremony than a surgical operation). Although as India becomes more modernised, westernised and secular, attitudes to the hijras are changing, their traditional role has existed for centuries in a culture where transgendered individuals were viewed as meaningful, even powerful. Their income mostly comes from performing at, and thus blessing, weddings and births, both of which celebrate the union of male and female. There is an irony about this, of course, since the one area of traditional Indian life they can never enter is that of marriage and children, but their power to bless derives from the fact that, like the gods, they unite the principles of male and female within them.

But why should such tolerance exist in societies which have hardly been exposed to many of the egalitarian advances in gender relations that are taken for granted in the West? Perhaps the answer is that academic discourses on sex and gender have tended to concentrate rather heavily on economic, political, and social aspects of sex and gender issues to the detriment of the imaginative and spiritual worlds which underlie the more visible institutional structures and have undeniable significance. The Bible, for example, inhabits (and thereby promotes) a strictly binary world. The sexes are resolutely divided. Animals enter the Ark in their famous two-by-two formation, a division sanctioned by the Genesis creation story of 'male and female created He them'. Catholicism may have the rather sexless Mary as a female exemplar, but in the Protestant creeds there are no core female figures at all. This is in stark contrast to religions such as Hinduism where there are not only female deities but also many examples of figures from religion and mythology moving between male and female.

But even if we allow for the influence of such religious instruction upon our tendency to see the world in binary gender terms, it still seems odd that a society which is now so accepting of pre-marital sex, homosexuality, and the ready availability of sexually explicit images should still be so prepared to censure by ridicule those men who wish to cross-dress. Why should we continue to allow ourselves to be locked into a world of regularities? Why would we want to? As sociologist Holly Devor comments: "We have begun to acknowledge the extraordinary bio-diversity around us in the world - together with an understanding of the need for its survival if the planet is to thrive - but unfortunately we have been very slow to generalise this concept to our understandings of gender, sex and sexuality. We tend to think of people whose gender, sex or sexuality are unusual as 'mistakes' of either nature or nurture."

Perhaps what our attitude to transvestism tells us about most clearly is our deep-down attitude towards women. Masculinity is still the 'must-have' factor in so many of the achievements that our culture prizes. In such circumstances, how can we possibly understand those who would voluntarily surrender this valued asset? We may have abandoned many of our preconceptions about the nature of the female but we still can't understand why on earth any man would want to be taken for one. Boys who want to play with girls' toys are somehow 'downgrading' themselves.

Some comfort may be derived from this research in that many transvestites, despite the adversities that they have had to overcome, can still acknowledge a positive side. Like Shakespearean heroines who grow through the experience of becoming temporary males, those who cross gender boundaries report that it gives them an experience of the 'other' which widens their view of the world and their place within it. What a pity that we should regard their wish to go on behaving that way as either ridiculous or incomprehensible.