Project Summary Studies on the health effects of sex tourism report that sex workers are one of the most vulnerable groups for acquiring HIV due to their high rates of sexual risk behaviors1 and their disadvantaged positions to negotiate safe sex because of social, economic, and cultural factors.2 In low prevalence countries with concentrated epidemics, HIV prevalence rates among sex workers are often 3 to 4 times that of the general population.3 This risk is often perpetuated by the availability and accessibility of illegal drugs in tourism zones. While studies have examined the association between HIV risk-related behaviors including drug use and sexual risk-taking and the social and physical environment that characterize neighborhoods;4, 8-11 there is a fundamental gap in the current scientific evidence-base about which extra-individual contexts, ?activity spaces? (spaces in which daily activities occur) and social interactions or networks interact, and how that impacts HIV risk behavior. The goal of the proposed research is to utilize innovative spatial-temporal and social network methodology to describe the relationship between activity spaces and social network characteristics of male migrant sex workers in tourism zones in the Dominican Republic (DR), and to assess how such daily activity patterns and networks jointly affect HIV risk behavior, testing and infection. Considering that the DR has one of the largest sex tourism industries in the Caribbean and is currently experiencing a dramatic increase in the use and transport of illegal drugs, spurred by a shift in smuggling routes to the United States,27, 28 the country provides a unique environment for examining how environmental and social structures shape HIV risk and related behaviors among sex workers. A deeper understanding of the multiple factors that influence day-to-day experiences of male migrant sex workers is paramount for reducing the HIV burden in the DR, and for preventing international transmission through tourism and migrant routes. This study has three specific aims: (1) To utilize novel spatial-temporal methodology to characterize the activity spaces of male migrant sex workers in the Dominican Republic by linking activity space GPS data to already collected, novel ethnographic mapping data from a current NIDA-funded R01, and to examine the impact of risky activity spaces on HIV risk and related behaviors, specifically drug use, risky sex, HIV testing, and self-reported HIV; (2) To describe the social networks (e.g. size, composition) of male migrant sex workers, and assess the role social networks have on HIV risk and related behaviors in this population; (3) To examine the interaction between daily activity space and social network characteristics on HIV risk and related behaviors. If activity spaces can be identified and play a significant role in drug use and other HIV-related behaviors?including their combined role with network characteristics?it will provide critical information for creating effective structural and interpersonal HIV prevention interventions. To address the current barriers to HIV prevention and treatment, it is paramount that we focus not only on multiple social determinants, but also on the social experiences and lives of at risk populations.