Gamma-delta (gamma/delta) T cells are thought to represent the first line of defense against various pathogenic microorganisms. The aim of the present study was to investigate whether gamma/delta T cells were increased in BAL fluid (BALF) of patients with diffuse panbronchiolitis (DPB), a model of chronic lower respiratory tract infection. The study population consisted of four groups, including patients with DPB, sarcoidosis, idiopathic pulmonary fibrosis, and normal subjects. Two-color direct immunofluorescence and flow cytometry were used for analysis of peripheral blood or BALF from these patients. The percentage of peripheral blood or BALF gamma/delta T cells relative to the total number of lymphocytes was similar in the four groups. Although the absolute number of gamma/delta T cells in BALF was significantly higher in DPB patients compared with the other three groups, the total lymphocyte number in BALF in DPB patients was increased and the number of BALF gamma/delta T cells correlated with the total lymphocyte number in BALF. Furthermore, the percentage and number of BALF gamma/delta T cells were not related to a certain group of pathogenic organisms or the number of colony-forming units. Our results suggest that gamma/delta T cells are unlikely to play a part in chronic lower respiratory tract infection.