DESCRIPTION: (Applicant's Abstract) Injection drug use accounts for nearly one third of AIDS cases in the United States through direct or indirect transmission to other injection drug users, their sexual partners and offspring. In 1996, in states with confidential HIV testing, injection drug use or sexual contact with an injection drug user accounted for 35% and 86% respectively, of new HIV-positive tests in men and women whose risk category was reported. In response, the National Academy of Sciences recommended in 1995, that HIV prevention strategies among injection drug users in the United States should include both needle exchange programs and deregulation of prescription and paraphernalia laws. Some U.S. states (e.g. Connecticut) have already implemented both these recommendations, and more are on the way to doing so. Despite widespread access to sterile syringes through established needle exchange programs and pharmacy access, there is recent evidence of high HIV infection rates among injection drug users in Montreal (5% per year) and Vancouver (19% per year). The purpose of this study is to follow well established cohorts for trends in seroincidence and to identify factors and processes which explain these elevated HIV infection rates among populations of injection drug users who have access to sterile injection equipment. The major hypothesis under study is that a complex relationship of factors, social dimensions and processes including the type of drug, the pattern of drug use, the micro social climate surrounding the user, the macro-social climate in the drug using community, and attitudinal factors create situations of sub-optimal utilization of sterile injection equipment, which in turn impact upon HIV incidence rates among injection drug using populations. We hypothesize these factors and processes may be so potent that they can outweigh the protective effects of needle exchange and legal pharmacy access. The study will use both quantitative (epidemiologic cohort) and qualitative (life-history interviews, ethnography) methodologies to study well-established groups of injection drug users in Vancouver and Montreal. The two site nature of the study will allow comparisons within and between these cities in an effort to identify common and divergent risk factors, protective factors and processes related to sub-optimal syringe utilization and increased risk of HIV infection. Explaining the reasons why needle accessibility alone is not sufficient to halt HIV transmission in injection drug using populations is of paramount importance. Such findings could help jurisdictions in the U.S. and elsewhere to avoid a repeat of our recent experience.