role. The second explanation is that homeless individuals represent the tenants of choice, occupying housing developed specifically for low-income occupants. Methodologically, testing these theories requires longitudinal data on housing value and occupancy, as well as complete data on last stable housingand individual-level characteristics for a representative homeless sample. Using a uniquedata set, Service Use, Needs, Costs, and Consequences of Drug Abuse on homelessness (SUNCODA: R01-DA 10713), we propose to combine the last stable addresses for 400 randomly-sampled homeless with publiclyavailable (but unfortunately low technology) housing stock information, controlling for census-level data for the relevant zip code, in order to test the study hypotheses. The two proposed theories have strong implications for current service use models and development of primary prevention efforts. Because current services focus on housing as a primary outcome, finding that multiple risk factors lead to housing that is likely to become unstable represents critical new informationfor improving current services. Thus, this proposal is responsive to the PA-02-150, Services and Intervention Research with Homeless Persons havingAlcohol, DrugAbuse, or Mental Disorders.

Scavenger receptors (SR) are cell surface proteins that bind chemically modified lipoproteins and exhibit broad ligand binding specificities. We have identified three classes of vertebrate and invertebrate SRs: class A (SR-A), class B (SR-B) and class C (SR-C). They participate in or influence lipoprotein metabolism, development, host defense (innate immunity, protection against septic shock and viral infection), possibly asbestosis, recognition and clearance of damaged (apoptotic) cells and macromolecules, red blood cell maturation, female fertility and atherosclerosis/coronary heart disease (CHD). Many of their functions are directly related to health and disease and are consequences of their broad ligand binding specificities. One of these, SR-BI, is a physiologi