During past, present, and future Adult AIDS Clinical Trials Group (AACTG) clinical trials, samples of HBM (e.g., blood, other body fluids and tissues) have been or will be obtained and stored until analyzed, as defined by the particular trial for which the patient provided consent. Some HBM may be left over after a trial is completed. Important questions may arise during the design of a study; some of these questions may be addressed only with archived (rather than prospectively collected) HBMs. To improve understanding of HIV disease and its optimal management, it is critical that HBMs be available to investigators for subsequent unspecified analyses.