T-lymphocytes with T-cell antigen receptor (TCR) comprising a γ chain and a δ chain (γδ+ T cells) are believed to be involved in the immune reaction to mycobacterial antigens, and they have been found in increased proportions in sarcoid patients. We evaluated the proportions of γδ+ T-lymphocytes and of two major γδ+ subpopulations, the Vδ1+ and the Vδ2+ T-cell subsets, in 10 normal blood donors, in 15 patients with tuberculosis (TB), seven of whom had pleural effusion (PE), and in 12 patients with pulmonary sarcoidosis (PS), nine of whom underwent bronchoalveolar lavage (BAL). T-cell subsets were evaluated in peripheral blood (PBL) of all subjects and in PE from patients with TB and in BAL from patients with PS. Compared with normal blood donors, patients with TB had increased proportions of PBL CD3+ γδ+ T cells (6 ± 1% versus 14 ± 3% of CD3+ T cells, p < 0.05) because of the presence of four patients who had an increase (respectively, 18.3, 22.0, 24.2, and 35.4% of CD3+ T cells) of γδ+ T cells. In patients with TB and PE, γδ+ T cells were 7.9 ± 2.7%, a value not different from that in the tubercular PBL and in normal PBL. Although patients with PS had proportions of PBL γδ+ T cells (9.2 ± 3.4%) similar to those in normal PBL, two patients had increased (35 and 31%) PBL γδ+ T-lymphocytes. The proportions of γδ+ T cells in sarcoid lung recovered by BAL were similar to those in PBL from patients with PS (3.0 ± 0.8% of CD3+ T cells, p > 0.05). Among γδ+ T-cell subsets, Vδ2+ T-lymphocytes were 73 ± 9% of total γδ+ T cells in PBL of normal subjects, similar to PBL and PE of patients with TB and to PBL and BAL of patients with PS. However, in the patients with TB or PS with an expansion of PBL γδ+ T cells, Vδ2+ T cells were > 90% of γδ+ T cells, and they were increased also as absolute numbers of cells/μl of PBL, whereas the proportions of Vδ1+ T cells were similar to normal values. The expansion of γδ+ T cells with identical variable regions in some patients with PS and TB may be due to similar immunopathogenetic processes and/or it may represent a type of immune reaction of a subgroup of patients.