The ATHOS (AIDS Time-Oriented Health Outcome Study) Program proposes continued development of prospective, longitudinal data sets of AIDS, ARC, HIV-positive, and at-risk subjects which contain clinical, laboratory, therapeutic, economic, and life-quality data. Patients are consecutively enrolled from five private practices and from community clinics through their physicians who are participating investigators. Complete patient confidentiality is maintained. The program is based upon 15 years experience with the Arthritis, Rheumatism, and Aging Medical Information System (ARAMIS), the 17-center, national arthritis data resource, the staff, quality control, outcome assessment, and follow-up protocols of that program, upon five years of prior data collection on AIDS and at-risk subjects, and on three years experience with the ATHOS program. Data are collected and maintained on microprocessors in physician offices and transferred, maintaining confidentiality, to Stanford for analyses. Standard protocols for data collection are developed and in place in all sites. Projected analyses include study of factors influencing transitions between clinical states, factors affecting life quality, comparison of outcomes in the private community as compared with clinic-based health care services, assessment of direct and indirect costs, factors influencing costs, efficacy of treatment programs (both approved and unapproved) in the affected community, and toxicity of therapy. Careful study of management, costs, and outcomes in the private sector will assist in development of recommendations for deployment of public resources. Currently there are more than 4,500 subjects in ATHOS. Patient enrollment is anticipated at over 2,500 in the next two years for a total of 7,000 to 8,000 patients. The proposed addition of a new data bank site will broaden the ethnic and gender mix in ATHOS. The program addresses AHCPR AIDS priorities for studies of costs and financing, stages of illness, development of HIV information systems, and development of AIDS research methods based on chronic disease data bank systems.