Five biopsy specimens of skin, four of lung, and one of a lymph node were taken from nine patients with sarcoidosis. Monoclonal antibodies were applied to frozen sections of the specimens by an immunoperoxidase technique to test for the presence and distribution of subsets of T-lymphocytes. T-cells expressing the suppressor/cytotoxic phenotype were found predominantly in lymphocytic mantles surrounding sarcoidal granulomas, whereas cells displaying the helper/inducer phenotype were distributed diffusely throughout granulomas. The ratio of helper to suppressor phenotypes in cutaneous sarcoidosis was 5.1 ± 1.8. The microanatomic location of subpopulations of T-lymphocytes may be important in the pathogenesis of the granulomatous response of sarcoidosis.