Tuberculosis can affect calcium metabolism, mainly through an enhanced production of active vitamin D. The incidence of hypercalcemia among unselected patients with active pulmonary tuberculosis was investigated, retrospectively, during a ten-year period. Among 67 patients, the mean serum calcium concentration on admission was significantly raised compared to healthy controls (2.51 +/- 0.16 (SD) vs 2.43 +/- 0.07 mmol/l; p less than 0.001) and 25% of the patients had hypercalcemia. After one year of successful tuberculostatic treatment the serum calcium values had normalized.