Glucose is absorbed from the dialysate more rapidly in younger than in older children on CAPD leading to a relatively early loss of ultrafiltration during dwell time. In order to assess peritoneal permeability and in term to prescribe optimal management of CAPD, we tested peritoneal equilibration curves (EC) for urea and glucose, especially the crossing time point of these two ECs. Baseline values were obtained from 8 patients divided in two groups by age at start of CAPD: group I (N = 4) mean age 1 year 6 months, mean body weight 8.25 +/- 3.17 kg, group II (N = 4) mean age 12 years 6 months, mean body weight 33.5 +/- 1.5 kg. The crossing time point is earlier in group I (49 +/- 14 min) than in group II (101 +/- 20 min) (p less than 0.001). Followup of each patient, during a mean time of 20 months in group I and 23 months in group II, establishes that the curves crossing time point for each patient remains stable.