This pilot study was designed to evaluate the efficacy and acceptability of sevelamer hydrochloride as a phosphate binder in pediatric patients treated with dialysis. A 6-month open-label trial of sevelamer hydrochloride (Renagel) was initiated in 17 patients, aged 11.8+/-3.7 years, undergoing hemodialysis ( n=3) or peritoneal dialysis ( n=14). Following a 2-week washout period of the phosphate binders, serum phosphorus increased from 5.2+/-1.3 mg/dl to 7.5+/-2.2 mg/dl ( P<0.0002). After initiation of therapy with sevelamer hydrochloride, serum phosphorus levels decreased to 6.2+/-1.2 mg/dl ( P<0.01) during the first 8 weeks and final values were 6.3+/-1.5 mg/dl. Serum calcium concentration decreased during the washout period from 9.4+/-0.9 mg/dl to 8.9+/-1.5 mg/dl ( P<0.01); values remained unchanged thereafter. The serum calcium-phosphorus ion product decreased during the first 8 weeks and values did not change subsequently. Serum bicarbonate, parathyroid hormone, total cholesterol, low-density lipoprotein and high-density lipoprotein cholesterol, and triglyceride levels did not change. The initial prescribed dose of sevelamer hydrochloride was 121+/-50 mg/kg (4.5+/-5 g/day) and the final prescribed dose was 163+/-46 mg/kg (6.7+/-2.4 g/day). Sevelamer hydrochloride was well tolerated and without adverse effects related to the drug.