Vitamin D metabolites in serum and calcitriol receptor concentration in parathyroid tissue were examined in 52 patients operated on for primary hyperparathyroidism. The calcitriol receptor levels were not different in parathyroid adenomas (mean 224 fmol/mg of protein, range 29-509, N = 43), normal parathyroid tissue (mean 245, range 31-690, N = 20), and primary parathyroid hyperplasia (mean 172, range 46-477, N = 9). Preoperative serum levels of calcitriol concentration correlated inversely to the calcitriol receptor in normal parathyroid tissue in patients with adenoma (r = -0.57, N = 17, p = 0.017), but no such correlation was found in the corresponding adenomas (r = 0.14, p = 0.59). In 31 patients in whom both pre- and postoperative vitamin D metabolite analyses were carried out, 23 had lower calcitriol postoperative concentrations compared to preoperative values (p = 0.012, sign test). No change was found in the other vitamin D metabolites postoperatively. By multiple regression analysis calcitriol concentration in serum was inversely correlated to the serum concentration of urea and phosphate (p = 0.003). We conclude that calcitriol may influence calcitriol receptor expression in normal parathyroid tissue, but not in adenomatous parathyroid gland. Furthermore, serum calcitriol was correlated to the renal function, and phosphate level, and in most patients the calcitriol concentration was lower after the operation.