Oxalate elimination and oxalate dialysance via hemodialysis (HD) or peritoneal dialysis (CAPD) has not been studied in detail in pediatric patients. We studied plasma oxalate, oxalate elimination, and oxalate dialysance in 15 infants and children undergoing CAPD (9 female, 6 male, aged 9 months to 18 years) and in 10 children on HD (4 female, 6 male, aged 7-18 years). Two children in each group had primary hyperoxaluria (PH). The mean duration of dialysis prior to examination was 12 +/- 11 months in CAPD and 31 +/- 23 months in HD patients. Bicarbonate HD was performed 5 h three times a week, CAPD consisted of five daily exchanges in 5 patients and four changes in the remaining 10 children (dwell volume 40 ml/kg body weight, 2.3 g/l glucose). Although oxalate dialysance was significantly higher in HD (mean 115.6 ml/ min per 1.73 m2 in HD versus 7.14 ml/min in CAPD), mean oxalate elimination per week was not different between both renal replacement therapies (3,478 mumol/1.73 m2 surface area/week in CAPD versus 3,915 mumol/1.73 m2 per week in HD). Oxalate elimination in patients with PH was between 6,650 and 9,900 mumol/week. Plasma oxalate remained elevated in both procedures [28-84 mumol/l in CAPD (92/148 in PH) and 33-101 mumol/l in HD (70/93 in PH)]. Oxalate elimination can be increased by a more frequent hemodialysis regimen.