Lymphocyte subpopulations in the intestinal tissues of seven patients with acquired immunodeficiency syndrome (AIDS) or AIDS-related complex (ARC) were studied by immunohistologic technics at two different locations, the small bowel and the rectum. Intraepithelial and lamina propria lymphocyte subsets stained with monoclonal antibodies T11, T4, T8, and B1 were enumerated in the patients and different normal and patient control groups. Intraepithelial T11+ cells were decreased (P less than 0.05) in the small bowel of AIDS and ARC patients, primarily because of the near complete absence of T4+ lymphocytes. In the lamina propria of these patients, a depletion of T4+ cells (P less than 0.05), an increase in T8+ cells (P less than 0.05), and a reversal of the T4/T8 ratio were observed (e.g., the small bowel ratio was 0.1 +/- 0.02 vs. the normal ratio of 2.3 +/- 0.2 and the rectal ratios were 0.2 +/- 0.06 vs. normal 2.6 +/- 0.3). The T-lymphocytes in the intestine of AIDS and ARC patients did not express the receptor for interleukin-2 (IL-2). A near complete absence of T4+ lymphocytes was also seen in lymphoid follicles in the rectum. B1+ cells were not depleted. The reversal of the T4/T8 ratio, which is a hallmark of AIDS, occurs not only in the circulation but also in the gastrointestinal tissues of patients with AIDS and ARC.