The aim of this study was to investigate the relationship between the pulmonary vitamin D metabolism in tuberculosis and the calcium metabolism abnormalities and other clinical characteristics of the disease. The metabolism of 25-hydroxyvitamin D3 (25(OH)D3) by alveolar immune cells recovered by bronchoalveolar lavage (BAL) was evaluated in parallel to the results of calcium metabolism, 25(OH) D and 1,25 dihydroxyvitamin D (1,25(OH)2D) plasma levels and other clinical parameters obtained in 14 tuberculosis patients. Whilst predominant metabolites produced by lavage cells in patients and controls were 5(E)--and 5(Z) -19-nor-10-oxo-25(OH)D3, 1,25(OH)2D3 was produced by cells from all tuberculosis patients but not by cells from controls. Calcium metabolism abnormalities were observed in only some patients, but the production of 1,25 (OH)2D3 by lavage cells was found to correlate both with 1,25(OH)2D levels (r = 0.67) and post-load urinary calcium excretion (r = 0.59). 1,25(OH)2D3 production by lavage cells was increased in patients of black origin, and those presenting with hilar adenopathy without pulmonary infiltrates, and was correlated with the number of lymphocytes recovered by lavage (r = 0.87). We conclude that 1,25(OH)2D3 production by alveolar immune cells makes a major contribution to the abnormalities in calcium metabolism seen in tuberculosis patients, and may be partly dependent on the clinical characteristics evaluated here.