To investigate the extrarenal production of 1,25(OH)2D3 in tuberculosis, we extensively evaluated a patient with tuberculosis, hypercalcemia, and an elevated plasma concentration of 1,25(OH)2D3. Fresh total cells and cultured alveolar macrophages obtained by bronchoalveolar lavage were demonstrated to synthesize 1,25(OH)2D3 prior to and after nine months of successful antituberculous therapy. The continued capacity to produce 1,25(OH)2D3 was associated with a persistent lymphocytic alveolitis in this patient. This extrarenal production of 1,25(OH)2D3 probably contributed to the increased levels of plasma 1,25(OH)2D observed in our patient. Nevertheless, a close correlation between plasma 1,25(OH)2D and serum calcium was not observed. These findings suggest that although extrarenal production of 1,25(OH)2D3 occurs in tuberculosis, it need not be a predominant factor producing the abnormalities in calcium homeostasis observed in such patients.