The French SEROCO and HEMOCO hospital-based cohorts have enrolled and followed HIV-infected patients, before and after the highly active antiretroviral therapy era. Among the objectives in 1988, was explicitly mentioned the constitution of a centralised bank of biological material (serums at enrollment and every 6 months, PBMC at enrollment and every 18 months). This paper details the organisation of the bank and the numerous studies performed from this bank, and presents a few simple decision rules which have been developed with the growing acquired experience.