Before December, 1986, all public human immunodeficiency virus (HIV) testing in Oregon was done confidentially (using names). In December, clients were offered the option of either anonymous or confidential services. As judged by questionnaire responses, the availability of anonymity increased overall demand for testing by 50%: 125% for homosexual/bisexual (gay) men, 56% for female prostitutes, 17% for intravenous drug users, and 32% for other clients. The number of gay clients who had tests increased from a mean of 42 per month during the 4 months before anonymity was available to 108 per month during the 4 months after, whereas, at public sites in Colorado or California and private sites in Oregon, the number of gay clients tested did not increase. Twice as many seropositive persons were identified during the 3 1/2 months after anonymity became available (n = 85) as in the 3 1/2 months before (n = 36). Thus, availability of anonymous HIV testing and counselling drew gay men who had not sought services under a confidential testing system.