Recent research with homosexual samples in San Francisco (Stall, McKusick, Wiley, Coates,&Ostrow, 1986) has shown that the use of alcohol (or other drugs) in conjunction with sexual activity is strongly related to unsafe sex (i.e., high risk for AIDS infection). Analysis of data from a mail survey of the adult population of San Francisco replicated these results: There was a strong relationship between frequency of using alcohol or other drugs in conjunction with sexual activity and the frequency of engaging in risky sexual behaviors. However, risky sexual behavior wasnotrelated to theproportionof sexual activity involving drinking andwasrelated toproportionof sexual activity involving cocaine and other drugs in gay men only. Frequency of risky sex in hetersexuals was predicted largely by total frequency of sex, with small amounts of variance contributed by frequency of sex with a partner who was drinking or using drugs. In gay men, use of cocaine or other drugs during sex contributed a substantial amount of explained variance in risky behavior.