The known relationship between peritoneal fill volume (IVP) and dialysis efficiency favors the use of an optimal IVP to enhance peritoneal dialysis (PD). Therefore, we have studied the effects of an increased IVP in consecutive stages [800, 1400, and 2000 mL/m2 of body surface area (BSA), respectively] in 8 children on chronic PD (mean age: 9 years 6 months; range: 2-16 years). Each prescribed IVP was maintained for 60 minutes of dwell time, allowing a short peritoneal equilibration test. Tolerance was assessed clinically and by intraperitoneal pressure (IPP) measurements at the end of each dwell test. Determination of dialysate-to-plasma ratios, and calculation of mass transfer area coefficients (K0A) using the Henderson method for urea, creatinine, and phosphate, were used to assess the impact of an increased IVP on dialytic efficiency. Increasing IVP from 800 to 1400 and thereafter to 2000 mL/m2 induced an IPP increment, respectively, from 8.4 +/- 1.4 cm (of water) to 12.1 +/- 1.4 cm and thereafter to 18.3 +/- 1.4 cm, with a positive strong linear correlation (r = 0.92; P = 0.001; IPP = 1.46 +/- 8.17(-3) IVP). In the same manner increasing IVP induced K0A increments for urea of 10.6 +/- 1.2 mL/min per m2 to 15.3 +/- 1.6 mL/min per m2 and 17.1 +/- 1.9 mL/min per m2; for creatinine of 7.9 +/- 0.09 mL/min per m2 to 11.2 +/- 0.18 mL/min per m2, and 12.3 +/- 0.21 mL/min per m2; and for phosphate of 5.2 +/- 0.08 mL/min per m2 to 6.7 +/- 0.09 mL/min per m2 and 6.6 +/- 0.07 mL/min per m2, respectively. When K0A values were normalized to the values achieved at the IVP of 1400 mL/m2, the K0A gain obtained increasing IVP from 1400 to 2000 mL/m2 was only significant for urea, peaked for creatinine, and even slowly decreased for phosphate. Moreover, a fill volume over 1400 mL/m2, which appears to be the optimal volume in terms of dialysis efficiency, was only barely tolerated with clinical signs of discomfort and an increased IPP. Therefore, in our opinion, the maximal IVP in children over the age of 2 years should be nearly 1400 mL/m2, both in terms of abdominal tolerance and in terms of urea, creatinine, and phosphate peritoneal membrane purification capacities.