Accurate characterization of peritoneal solute transport capacity in children has been hampered by a lack of standardized test mechanics and small patient numbers. A standardized peritoneal equilibration test was used to study 95 pediatric patients (mean age, 9.9 +/- 5.6 yr) receiving chronic peritoneal dialysis at 14 centers. Patients were divided into four age groups (< 1, 1 to 3, 4 to 11, 12 to 19 yr) for analysis. Each patient received a 4-h peritoneal equilibration test with an exchange volume of 1100 mL/m2 per body surface area. Dialysate to plasma (D/P) ratios for creatinine (C) and urea (U) and the ratio of dialysate glucose (G) to initial dialysate glucose concentration (D/D0) were determined. Mass transfer area coefficients (MTAC) were calculated for the three solutes and potassium (P). The mean (+/- SD) 4-h D/P ratios for C and U were 0.64 +/- 0.13 and 0.82 +/- 0.09, respectively. The mean 4-h D/D0 for G was 0.33 +/- 0.10. D/P and D/D0 ratio results were similar across age groups. Normalized (for body surface area) mean MTAC (+/- SD) values were as follows: C, 10.66 +/- 3.74; G, 12.93 +/- 5.02; U, 18.43 +/- 4.02; and P, 14.02 +/- 3.94. Whereas a comparison of the normalized MTAC values across age groups with an analysis of variance showed significant age group differences only for glucose (P = 0.001) and potassium (P = 0.036), analysis by quadratic regression demonstrated a nonlinear decrease with age for C (P = 0.016), G (P < 0.001), and P (P = 0.034). In summary, evaluation of D/P and D/D0 ratios obtained from a large group of children in a standardized manner reveals values that are similar across the pediatric age range and not unlike the results obtained in adults. In contrast, normalized MTAC values of young children are greater than the values of older children, possibly as a result of maturational changes in the peritoneal membrane or differences in the effective peritoneal membrane surface area.