The proposed research is designed to study the sexual and drug networks of US long-haul truckers and their potential role in the acquisition and dissemination of sexually transmitted and blood-borne infections. It builds upon and extends our small-scale studies with truckers, "truck chasers," and other trucker network groups that revealed extensive risk-taking, ranging from IDU to frequently unprotected sex. With primarily male heterosexual truckers at their center, trucker risk networks include such diverse groups as: men who have sex with men including "truck chasers" and sex workers (CB hustlers, "buffaloes"); female sex workers (CB prostitutes, "lot lizards," "traveling ladies," American and Mexican brothel workers, motel sex workers, street walkers/hustlers); female "truck chasers;" drug dealers/pushers/runners and pimps; "polishers," "lumpers," homeless, and hitchhikers; trucking company and truck plaza employees; home setting social and risk contacts; and other sexual and drug contacts on the road. Despite demonstrated links between trucking routes and STI/HIV transmission in other parts of the globe, and truckers' potential role as bridges between populations with significant structural equivalence within truck plazas and other highway trucker settings in the US, there exists a research lacuna in the potential public-health repercussions of the constant movement of 3.3 million US. long-haul truckers. A combination of qualitative and quantitative designs and methodologies as well as biological testing are planned to achieve four specific aims: 1) the comprehensive ascertainment of how truckers' work milieu, interpersonal relationships, social network configurations, and home settings influence their drug use and sexual behaviors, placing them at risk for acquisition of STI/HIV and other blood-borne and sexually transmitted infections; 2) the establishment of baseline seroprevalence of HIV, HCV, HBV, syphilis, gonorrhea, and Chlamydia among trucker risk-network members and groups to generate epidemiologic profiles of infection; 3) the analysis of ethnographic results of the core trucker risk-network members and groups as well as baseline seroprevalence, in terms of the influence of higher-order causal levels; and 4) the utilization of ethnographic findings to develop and pilot test both paper-and-pencil and computer-assisted personal interview (CAPI) versions of a survey instrument to assess truckers' risk taking, their highway, social and risk networks, and the acquisition of STI/HIV and other blood-borne and sexually transmitted infections. The successful implementation of these aims will be instrumental in generating long-overdue epidemiologic estimates of US. trucker networks' risk-taking via a cohort prospective study and in initiating an assessment process that will lead to risk/infection/disease mapping across trucking routes as well as risk reduction interventions.