To evaluate the characteristics of peritoneal kinetics in the young, we investigated solute and water transfer rates by a modified Peritoneal Equilibration Test (PET) in 20 pediatric patients aged 1.9 to 19.8 years. 1000 ml/m2 body surface area of a 2.3% glucose PD solution were instilled in the peritoneal cavity. Glucose, creatinine, urea, sodium, potassium and phosphate were measured in the dialysate (D), 7 times during 4 hours and in plasma (P) after 2 hours dwell time. At 4 hours, the mean (+/- SD) D/P ratio was 1.06 +/- 0.16 for urea, 0.79 +/- 0.14 for creatinine, 0.82 +/- 0.21 for potassium, 0.92 +/- 0.04 for sodium and 0.79 +/- 0.30 for phosphate. Mean D/D0 of glucose was 0.36 +/- 0.13. The 4-hour solute equilibration curves were analytically best approximated by logarithmic functions for urea (mean R2 = 0.983), creatinine (R2 = 0.973) and potassium (R2 = 0.979), by a linear function for phosphate (R2 = 0.964), and by an exponential model for glucose (R2 = 0.969). The linear or exponential regression coefficients were used to express the peritoneal solute transfer rates. Although the transfer rates of most solutes were correlated with each other, the individual variation of peritoneal permeability for different solutes was high. Close associations were observed between the glucose and creatinine transfer rates (r = 0.91, p < 0.0001) and between ultrafiltration rate and glucose (r = -0.90, p < 0.0005) and creatinine (r = -0.88, p < 0.005). Peritoneal permeability for all solutes tended to be inversely correlated with body size (urea transfer rate vs. height: r = 0.49, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)