HAART eligibility screening entails presenting to the study site within 2 weeks of pre-screening, undergoing laboratory testing and providing a medical history, and returning for results within the subsequent four weeks. Any potential subjects who appear to be acutely intoxicated will be asked to return the next day or at a later date or time of their choosing. All participants will be asked to return for their results within four weeks after screening. Subjects will have 70 mL of whole blood collected by venipuncture by a trained study nurse. Laboratory tests will include HIV confirmatory testing (antibody and Western blot), CD4 cell count and plasma HIV-1-RNA level (plasma viral load; pVL), Hepatitis A, B and C serology, pregnancy test for women of child-bearing potential, complete blood count (CBC) with differential and platelet count, chemistry profile (creatinine, urea and electrolytes), and transaminase levels (ALT, AST). All participants will also have a medical history taken and undergo a physical examination. Recorded data will include subject gender, age, ethnicity, race, area of residence and living arrangement (categorized as homeless/on the street, unstable [defined as living primarily in a single room occupancy hotel, boarding room, or transition house] or stable). Additional features which will be recorded will include nature and frequency of illicit substance use, and participation in other cohort studies or methadone maintenance programs. All clinical past medical history and co-morbidities and laboratory data will be recorded for assessment of subject HAART eligibility.