Project Summary CDC recommendations identify MSM in non-monogamous relationships and those in relationships with an HIV positive partner as candidates for PrEP. Estimates suggest as many as 79% of new HIV infections among young MSM (YMSM; ages 18-29) are transmitted between main partners. Drug use is an established correlate of HIV transmission risk. For partnered men, relational factors (e.g., sexual agreements) contextualize drug use and both drug use and sexual agreements predict receptivity to PrEP. Together, these findings point to the need for integrated intervention services – targeting drug use and sexual health –tailored for partnered YMSM. Such services are essential to addressing the HIV epidemic in the US. In response, our team has developed a 4-session MI-based intervention targeting PrEP uptake/adherence, HIV TRB, and drug use among partnered YMSM. PARTNER (Prevention And Risk: Treatment with a New Emphasis on Relationships) is delivered to individual YMSM in relationships (not couples), which enhances the scalability of the proposed intervention. Our preliminary pilot work has established the acceptability and feasibility of PARTNER. The primary goal of the current study is to test the efficacy of PARTNER relative to an attention-matched educational control condition used in previously funded NIH studies with HIV-negative YMSM. We propose to recruit 240 HIV-negative partnered YMSM who report recent drug use and sexual behavior consistent with CDC guidance for PrEP candidacy into a randomized control trial. As part of a secondary aim, this project seeks to enhance the range of biological measures for PrEP adherence currently available. The field standard for assessing tenofovir metabolites is dried blood spot assay; however, fingernail assay has high acceptability and lower cost. We propose to validate fingernail samples for PrEP adherence by correlating results obtained from fingernail samples with dried blood spot data. The study team is led by Dr. Tyrel J. Starks (PI), a new investigator with substantial experience in the study of relationship factors associated with sexual health and MSM in relationships. He has collaborated on numerous projects examining the nature of sexual agreements and their association with substance use and HIV transmission risk behavior. He is supported by a study team which includes Dr. Jeffrey Parsons, the PI of multiple intervention studies targeting sexual health and substance use. He is also joined by Dr. Monica Gandhi, an expert in biological assessment for PrEP adherence who has pioneered the use of novel matrices in previous NIH- funded studies. The team brings extensive experience in behavioral intervention research, relationship research, and biomedical assessment.