OBJECTIVE: Stimulant abuse is associated with an increased risk of contracting human immunodeficiency virus (HIV). Although sharing of contaminated needles is one of the routes by which HIV is spread, noninjection abusers are also at high risk. The authors investigated the effect of the stimulant drug methylphenidate (given intravenously) on sexual desire as a possible contributing factor to risky sexual behavior associated with the contraction of HIV. METHOD: The effects of intravenous methylphenidate (0.5 mg/kg) on self-reports of sexual desire (rated from 0-10) were evaluated in 39 comparison subjects and 39 cocaine abusers. RESULTS: Intravenous methylphenidate significantly increased self-reports of sexual desire in comparison subjects (1.4 versus 3.7) and cocaine abusers (2.8 versus 4.8). CONCLUSIONS: Stimulant-induced enhancement of sexual desire could be one mechanism by which stimulant drugs such as cocaine and methamphetamine increase the risk for HIV transmission even when they are not injected.