Several parameters of phosphocalcic metabolism were evaluated in 21 patients with active pulmonary tuberculosis. The serum levels of total calcium, ionic calcium, phosphorus, albumin, magnesium and alkaline phosphatase, and calciuria and calcium/creatinine ratio in 24-hour urine were normal and not change during therapy. The patients with tuberculosis showed a significant reduction in the 250HD concentrations (8.8 +/- 5.2 ng/ml vs 19.2 +/- 10.7 ng/ml; p = 0.002), 1.25(OH)2D (25 +/- 8 pg/ml vs 34 +/- 9 pg/ml; p = 0.002) and parathyroid hormone (intact molecule) (1.9 +/- 0.9 pmol/l vs 5.9 +/- 2.0 pmol/l; p = 0.0001). By contrast, the levels of calcitonin (65 +/- 30 pg/ml vs 36 +/- 17 pg/ml; p = 0.001) and tartrate-resistant acid phosphatase (17.3 +/- 2.3 U/l vs 11.8 +/- 1.8 U/l; p = 0.0001) were increased. There also was a mild increase of vitamin D carrier protein (532 +/- 109 mg/l vs 480 +/- 37 mg/l; p = 0.04). These data are consistent with a partial inhibition of parathyroid hormone, associated with vitamin D deficiency. The inhibition of the axis of parathyroid hormone--1.125(OH)2D resulting from calcium release from the bone is advanced as an explanation. This release might be due to the action on the bone of cytokines produced within the inflammatory process itself. The reduction in 250HD could presumably be related with the lower exposure to sun, which is common in sick persons.