Because gamma/delta T lymphocytes (gamma delta cells) respond to myco-bacterial antigens in vitro and accumulate in the skin lesions of patients with certain granulomatous infections (leprosy, leishmaniasis), it was hypothesised that these cells might have a role in the pathogenesis of sarcoidosis, a disease also characterised by granuloma formation. Having failed to demonstrate an increase in gamma delta cells in the blood of patients with sarcoidosis, the aim of this study was to examine samples of bronchoalveolar lavage (BAL) fluid and biopsy tissue. Samples from 23 patients (13 women) with newly diagnosed sarcoidosis, of mean age 31 years and median percentage of lymphocytes in the BAL fluid of 31%, were studied. Controls included normal subjects and patients with other interstitial lung diseases (ILD). Cytopreparations of BAL fluid (n = 13) and cryostat sections (five mediastinal nodes, 14 transbronchial biopsies) were stained with alkaline phosphatase-antialkaline phosphatase and monoclonal antibodies to CD3, CD4, CD8, CD25, and gamma delta T cell receptor (TCR). All patients had typical chest radiographs (16 stage I, four stage II, three stage III). All were Mantoux negative with negative tuberculosis cultures. Compared with normal controls and patients with other interstitial lung diseases there was no increase in gamma delta cells in the BAL fluid (sarcoidosis, 1% (range 0-4%) total cells; ILD, 1% (0-2%); controls, 0.5% (0-2%); p > 0.05, Kruskal-Wallis). Likewise, there was no increase in gamma delta cells in the transbronchial biopsy specimens (sarcoidosis, 1/high power field (hpf) (range 0-2); ILD, < 1/hpf (0-4); controls < 1/hpf (0-2); p > 0.05). gamma delta cells were rarely seen in the lymph nodes in spite of the presence of numerous granulomas. These results provide further evidence that gamma delta cells are not increased in most patients with sarcoidosis.