Studies in experimental animals have suggested that gamma/delta T-cells play an important role in the immune response against mycobacteria, but evidence for the participation of these cells in the course of human tuberculosis remains fragmentary. We have evaluated the number and state of activation of gamma/delta T-cells in the peripheral blood of patients with active tuberculosis using two-color cytofluorometry, and we have sought evidence that these cells might play a role in the impaired responses to recall antigens seen in some patients by comparing the proliferation of blood T-lymphocytes before and after removing gamma/delta T-cells by panning. Results were compared with those obtained for cells from normal subjects and from patients with sarcoidosis. The proportion and absolute number of circulating CD3+ gamma/delta T-cells were not significantly different comparing blood from patients with tuberculosis and that from control subjects [54.6 +/- 39.9 (n = 17) and 59.1 +/- 30.2 cells/microliters (n = 10), respectively, p > 0.2], and the proportion of cells expressing receptors using the V delta 1 variable region remained unchanged in patients with tuberculosis. Few gamma/delta T-cells from patients with tuberculosis expressed surface antigens associated with activation (IL-2R, < 1%; HLA-DR, 2.6 +/- 3.4%). Four of 15 patients with sarcoidosis had a proportion of gamma/delta T-cells that was outside the range observed in normal subjects, but the absolute number of CD3+ gamma/delta T-lymphocytes was not different comparing the two groups (p > 0.2).(ABSTRACT TRUNCATED AT 250 WORDS)