PIP: Recent developments concerning heterosexual transmission of HIV (review of 1988 literature only) suggest improved understanding of the pattern of spread and role of risk behaviors and biological cofactors in its transmission. 3 distinct patterns if HIV infection are known: heterosexual spread in sub-Saharan Africa and the Caribbean, spread primarily among homosexuals and injecting drug users in Europe, North American and much of Latin America and Australia, and both homosexual and heterosexual transmission in Asia, the Pacific, the Middle East and Eastern Europe, where prevalence is low. In Africa an estimated 80% of cases are acquired heterosexually. Important risk factors are number of sex partners, sex with prostitutes, being a prostitute, being a sex partner of an infected person, and having a history of other sexually transmitted diseases. Prevalence rates have risen rapidly in Zaire and Kenya. In Africa, acquisition of HIV is related to sexual activity only. In contrast, in the U.S., heterosexual cases make up only 4% of all cases, and in Europe only 6%. Data on types of sexual transmission of HIV are mounting, in aggregate suggestive of a marked heterogeneity in infectivity and possibly susceptibility between individuals. Among couples where the man is positive, in some places individuals appear to be highly infective, notably those from Kinshasa, Zaire and Haiti, while other series of discordant couples the receptive partner remained seronegative for several years. Transmission from women to men appears to be less efficient than from men to women, as has been observed with other STDs such as gonorrhea. Biological cofactors implicated in enhanced HIV transmission appear to be advanced CDC Stage IV AIDS disease, with low T-helper lymphocyte counts and high antigenemia; concomitant STDS, especially those with genital ulceration; lack of circumcision; oral contraceptive use; practice of anal intercourse; inconsistent or no use of condoms. Theoretical models for future heterosexual spread emphasize number of partners, use of condoms, and treatment of STDs.