Cases of AIDS have been reported in the U.S.A. since 1981 and its aetiological agent, human immunodeficiency virus type 1, HIV-1, has been spreading in the population for longer. A testing system was established at the hepatitis Reference Laboratory, HRL, to identify those infected in the Glasgow and West of Scotland population. The performance of commercial screening tests was examined using sera locally available at the HRL. Confirmation of reactivity was confirmed by western blot analysis; other methods of confirmation were examined. The criteria of positivity on a western blot were established from observation of the antibody response in seroconversion and weakly reactive samples compared to false reactive or indeterminate samples. In this way genuine HIV-1 infection could be reliably diagnosed
