We investigated phenotypic surface markers of peripheral blood lymphocytes including expression of γδ T cell receptor (TCRγδ) in 185 patients with sarcoidosis and 42 normal subjects. The proportion of TCRγδ+ lymphocytes in peripheral blood of patients with sarcoidosis (5.5 ± 5.4%) was significantly higher than in normal subjects (3.6 ± 2.2%; p < 0.05). A number of patients with sarcoidosis had prominently increased levels of circulating TCRγδ+ lymphocytes. Successive measurements of circulating TCRγδ+ lymphocytes demonstrated the persistence of increased levels of circulating TCRγδ + lymphocytes. We divided the patients with sarcoidosis into two groups, one with high, the other with low TCRγδ + expression. Compared with the low-value group, the high-value group had significantly decreased levels of circulating CD4+ lymphocytes, decreased incidence of a positive tuberculin reaction, and higher levels of serum angiotensin-converting enzyme and lysozyme, suggesting that these two groups may differ in their immunological response and disease activity of sarcoidosis. Measurement of TCRγδ+ expression in the circulation seems to be useful for estimating the disease activi