PROJECT SUMMARY/ABSTRACT Background: Miami-Dade County, FL (MDC) has the highest HIV incidence in the US. As of June 2017, 61% of new HIV diagnoses in MDC were attributed to Latinxs; and sexual contact with men who have sex with men (MSM) accounted for 92% of new HIV diagnoses among Latinx men. Of Latinxs diagnosed with HIV in 2017 in MDC, 85% were foreign-born. Alarmingly, new HIV diagnosis have increased 64% among Latinx MSM in MDC since 2010. While rates of PrEP usage in the US have significantly increased, only 6% of Latinx MSM were enrolled in a PrEP program in MDC. The Social Network Theory of Homophily can explain why these disparities impact LMSM communities so aggressively: similarities in characteristics between LMSM friendship dyads can impact the configuration of social networks. In turn, these network configurations can affect LMSM access to PrEP information, communication, and providers. The overarching goal of this F31 training program will be to study the effect of dyadic homophily (based on country of origin, immigration stress, Latinx cultural values, and substance use) on PrEP information within LMSM friendship networks and geographic accessibility to providers. The purpose of F31 training program is to sharpen my research skills and to provide the experiences for a career as an independent scientist well-qualified to obtain a postdoctoral position at a major research university. To pursue this F31 fellowship, I am supported by a strong team of Sponsors and a Senior Advisory Committee who will provide training in: 1) clinical research targeting the intertwining epidemics of HIV and substance use among MSM; 2) social network analysis to address Latinx health disparities; 3) comprehensive client-centered and culturally responsive LMSM PrEP services; and 4) geospatial analysis using GIS. Research component: I will conduct secondary data analyses using Dr. Mariano Kanamori’s (F31 Co-Primary Sponsor) project, PrEParados, with data specifically collected for this F31 application (N=156 LMSM grouped into 12 friendship networks). Aim 1 will determine whether homophily—based on country of origin, immigration stress, Latinx cultural values, and substance use—between dyads is associated with PrEP knowledge and communication within LMSM friendship networks. Aim 2 will determine whether the density due to homophily on LMSM dyads’ immigration stress, Latinx cultural values, and substance use is associated with geographic accessibility (walking, public transportation, and driving; times and distances) to available clinical PrEP services. The central hypotheses are that 1) there is an association between homophily on country of origin, immigration stress, Latinx cultural values, and substance use, and the configuration of social LMSM social networks, and 2) this social network configuration is associated with access to PrEP information within networks and geographic accessibility to PrEP providers. Significance: Findings of this F31 study will...