Calcitriol therapy is an important treatment for the prevention and control of secondary hyperparathyroidism in continuous ambulatory peritoneal dialysis (CAPD) patients. However, this often has been limited by the associated hypercalcemia and hyperphosphatemia due to increase in intestinal calcium and phosphorus absorption. Many studies reported that these limitations could be avoided by changing routes, frequency and dose of calcitriol treatment. But, there are still controversy about each methods and the results on the PTH response to conventional calcitriol treatment in CAPD patients. This study was performed to evaluate the factors affecting the response to oral calcitriol in CAPD patients. A retrospective study was done in 92 CAPD patients with secondary hyperparathyroidism(intact PTH level >200pg/ml) on oral calcitriol treatment. After baseline study of serum calcium, phosphorus, alkaline phosphatase, BUN, creatinine and intact PTH, calcitriol therapy was begun via oral rou- te, daily. Serum calcium, phosphorus, alkaline phosphatase, BUN, creatinine, intact FI'H and other bio- chemical markers were checked at 3 month, 6 month after treatment. Parathyroid gland ultrasonography was performed to detect parathyroid hypertrophy and nodule and to measure the diameter of parathymid gland. All the patients were divided into two groups according to percent reduetion of i-PTH(initial PTH PTH after 3, 6 months)X100/initial PTH(%),deltaPTH during oral calcitriol therapy for 3 and 6 months(group I ; delta PTH >30%, group II ; delta PTH <30%). RESULT: 1) All 92 patients(mean age 46.5 11.3yr, M: F 45: 47, mean CAPD duration 51.3 39.4 months) were administered oral calcitriol, daily. Mean calcitriol dose during 3 month was 0.43 0.22Mg and during 6month 0.43 0.24Mg. 2) After 3-month treament, there were significant differences in initial i-PTH, the diameter of parathyroid gland, initial phosphorus, intial total alkaline phosphatase and duration of CAPD between group I and II(406.7+/-196.5 vs. 871.0+/-478Apglml, 6.2+/-2.6 vs. 13.1+/-5.2mm, 5.0+/-1.3 vs. 5.7+/-1.3mg/dl, 93.7+/-4L1 vs. 171.9+/-137.6IU/L, 40.1+/-34.9 vs. 73.5+/-37.8months, p< 0.05, respectively). 4) After 6-month treament, there were significant differences in initial i-PTH, the diameter of parathyroid gland, intial total alkaline phosphatase and duration of CAPD between group I and II(474.1+/-266.6 vs. 889.7+/-485.4pg/ml, 6.4+/-2.7 vs. 14.5+/-5.1mm, 107.9+/-80.1 vs. 180.7+/-121.5IU/L, 40.5+/- 32.9 vs. 81.8+/-35.3months, p<0.05, respectively). 5) The significant negative correlation was shown between deltaPTH and the duration of peritoneal dialysis, the diameter of parathyroid gland, initial PTH level and PTH response during 3-month and 6-month oral calcitriol treatment. The response to oral calcitriol was poor when i-PTH level more than 500pg/ml(kappa 0.429, p value <0.01), the diameter of parathyroid gland more than 10.0mm(kappa 0.641, p value<0.01), the duration of CAPD more than 55months(kappa 0.524, p value< 0.01). These data suggested that initial i-PTH level, the diameter of parathyroid gland size and the duration of CAPD were independent risk factors of the poor response to oral calcitriol therapy in CAPD patients with secondary hyperparathyroidism.