some propositions on male and female sexual orientation will beconsidered. some of these are established; others are morespeculative. the aim is to offer some notes towards a coherent,comprehensive theory of sexual orientation. 1. the distinctionbetween butch and femme lesbians seems real rather than a socialconstruct. 2. high levels of prenatal steroid hormones seem to becausally associated with the sexual orientation of butch lesbians.however it is not established whether the causal process operatesprenatally or postnatally (or both). this is so because prenatalhormone levels are thought to correlate positively with postnatalhormone levels. and high postnatal hormone levels may facilitatehomosexual behaviour as a consequence of sensation-seeking. 3. malebisexuals also are interpreted to have been exposed to high prenataltestosterone levels. but (for reasons similar to those outlinedabove in regard to butch lesbians) it is unclear whether these havea direct prenatal effect on the brain or whether they are precursorsof high postnatal testosterone levels, which are associated withmale bisexual orientation by promoting sensation-seeking behaviour.4. postnatal learning processes seem to be causally involved in thesexual orientation of some femme lesbians and some exclusive malehomosexuals. 5. some homosexual men have genes that predispose totheir sexual orientation. 6. the same may apply to some lesbians,but such genes have not, as far as i know, been identified. 7.people (of both sexes) who engage in same-sex sexual behaviour maybe classified simultaneously in two ways, viz (1) ‘active’ vs‘passive’ and (2) those who do and those who do not engage (orconsider engaging) in sex with members of the opposite sex.ex hypothesi, some of the ‘active’ onesinitiate some of the ‘passive’ ones. the active ones are driven moreby hormones and the passive ones by psychosocial factors. the activemales contain a substantial proportion of self-identified bisexuals;and the active females a substantial proportion of self-identifiedbutches. 8. these two active categories (butch lesbians and malebisexuals) share a number of endocrinological, psychological,morphological and behavioural features vis-à-vis their exclusivelyhomosexual and heterosexual peers. methods of testing some of theseideas are presented.