Prediction of suitability of patients for tidal peritoneal dialysis (TPD) treatment based on the peritoneal equilibration test (PET) may be hypothetically subject to errors, due to the difference between the long equilibration times of the PET and the short dwell times currently utilized during TPD. Eleven patients, mean age 12.4 +/- 3.3 years, mean body weight 34.2 +/- 15kg, had both a standardized TPD run (initial fill volume 40 mL/kg, tidal volume 50%, dwell time 10 min, treatment time 8 h) and a PET performed. D/P ratios for creatinine and urea were calculated at the 5th and 7th TPD exchanges (approximating equilibration time of the TPD run), at the time points of the PET and on the total TPD dialysate volume. D/P ratios for creatinine and urea of the 5th and, even more, the 7th TPD exchange, and D/P ratios obtained from total TPD dialysate were significantly correlated overall (r = 0.96, p < 0.0001 for 5th D/P creatinine and urea; r = 0.98, p < 0.0001 for 7th D/P creatinine and urea). Correlation coefficients between PET-derived and total TPD dialysate-derived D/P ratios were generally poor or only modest. Thus, it is possible to predict TPD clearance, and consequently the suitability of patients for TPD, knowing the D/P ratios for creatinine and urea at the 7th TPD exchange of a standardized TPD run. Our data could represent a new reliable test for TPD prescription.