Methamphetamine abuse has a strong and consistent epidemiologic association with high-risk sexual behavior and both prevalent and incident HIV in men who have sex with men (MSM), and some authorities have advocated methamphetamine treatment as an HIV prevention strategy. However, methamphetamine interventions have not been evaluated in controlled trials, nor have they been implemented and assessed outside of substance abuse treatment programs. This application proposes preliminary investigations to adapt a methamphetamine treatment intervention previously associated with decreased sexual-risk taking among MSM for use as an early intervention among MSM in Seattle, Washington. Sixty methamphetamine-using MSM will be enrolled in a randomized controlled trial of contingency management (CM) versus no intervention. CM participants will have their urine tested for methamphetamine 3 times weekly for 12 weeks, and will receive vouchers of escalating value when their urines test negative; vouchers will be withheld when participants' urines test positive for methamphetamine or participants miss urine testing visits. All participants will undergo urine methamphetamine testing and audio-computer assisted self-interviews on sexual behavior and substance use at baseline and at 6 week intervals for 6 months. Participants will be tested for HIV, syphilis, rectal gonorrhea and chlamydial infection, and pharyngeal gonorrhea at baseline and at 3 and 6 month follow-up. The study will determine how often MSM will initiate and complete the early intervention, and will longitudinally measure unsafe sexual behaviors among intervention and control participants. Study results will determine the feasibility of instituting and studying CM as an early intervention; define whether the intervention is sufficiently promising to justify a larger, definitive randomized controlled trial; and will provide estimates for defining the number of participants such a trial would require.