This paper describes a retrospective evaluation of the course of renal bone disease in 14 children undergoing treatment with continuous ambulatory peritoneal dialysis (CAPD) for an average of 11.9 ± 1.5 months (mean ± SE). The patients were divided in two groups according to the changes in serum alkaline phosphatase activity during the period of observation: five patients had alkaline phosphatase activity that decreased or was relatively stable (group I), and nine patients exhibited a rising serum alkaline phosphatase activity (group II). Serial radiological examinations showed adequate control of renal osteodystrophy in the patients of group I, whereas the patients of group II had no improvement or worsening of their bone disease. Group I had higher serum calcium and lower parathyroid hormone levels than group II at the end of period of observation despite similar dosage of vitamin D metabolite. The progression of bone disease was not related to the duration of CAPD or type of previous treatment for end stage renal disease.The observation that the radiological manifestations of secondary hyperparathyroidism were prevented in patients whose serum calcium levels were frequently above 2.62 mmol/liter (group I) while serum calcium levels between 2.25 and 2.50 mmol/liter in group II patients failed to lead to regression of secondary hyperparathyroidism is consistent with the existence of altered “setpoint” regulation of the parathyroid gland in children undergoing CAPD.