The relationship between progressive immunodeficiency related to infection with human immunodeficiency virus (HIV) and waning immunity to measles was investigated in this retrospective cohort study. Titers of serum antibodies to measles virus were measured by enzyme immunoassay of stored sera from a cohort of homosexual men who were studied at San Francisco General Hospital. Subjects underwent a baseline and follow-up measure of measles antibodies. High levels of antibodies to measles virus were maintained in the HIV-positive and negative groups. One (2%) of the 50 HIV-negative controls was seronegative for the measles virus, and no controls evidenced seroreversal (decline in antibody to a level at which protection is not provided) during the study. Two (1.4%) of the 145 HIV-positive subjects were measles-seronegative, and two others evidenced seroreversal. Analysis with Spearman's rank correlation revealed no relationship between changes in the CD4 cell count and measles antibody level. Thus we conclude that waning measles immunity is not greatly accelerated in HIV-infected adults despite progressive HIV-related immunodeficiency.