Peritoneal fluxes of minerals and bone-modulating hormones and their impact on corresponding serum levels and bone mineralization in 7 children on continuous ambulatory peritoneal dialysis (CAPD) were studied. Most mass transfer studies revealed modest losses of calcium into peritoneal effluents. Peritoneal losses of phosphorus and magnesium, although substantial, were not sufficient to normalize hyperphosphatemia and hypermagnesemia in most patients. Parathormone and vitamin D metabolites (25-hydroxyvitamin D and 1,25-dihydroxyvitamin D) were readily detectable in peritoneal effluents. Improved bone mineral content, by sequential densitometries, was associated with amelioration of hyperparathyroidism. These data suggest that CAPD in children induces an overall improvement of disturbed mineral metabolism; nevertheless, peritoneal losses of calcium and vitamin D metabolites must be considered and replenished appropriately.