Secondary hyperparathyroidism (HP) is well known complication of long-term uremia. CAPD patients show a peculiar behaviour due to loss of vitamin D metabolites through peritoneum. Severe degrees of hyperparathyroidism may require parathyroidectomy in order to achieve appropriate control. Recently, the possibility of controlling this situation with high oral doses of calcitriol has been communicated. The purpose of this study is to evaluate the effect of this agent on hyperparathyroidism in CAPD patients. Two different groups were constituted according to the length of time on dialysis when HP was detected. All of the patients had i-PTH serum levels five times higher than the normal values (50 pg/ml). During a six month period the daily dose of oral calcitriol was increased in order to achieve a reduction in i-PTH level. The results after this period showed a significant reduction in i-PTH levels (614 +/- 378 to 241 +/- 80 pg/ml) with an average increase in oral calcitriol from 0.16 +/- 0.1 to 0.67 +/- 0.4 with no significant changes in serum calcium or phosphorus. The group with HP at start of dialysis achieved these effects easier and with lower doses of calcitriol. We conclude that moderately high doses of oral calcitriol control secondary hyperparathyroidism in CAPD patients without hypercalcemia.