Poor compliance in peritoneal dialysis (PD) is a significant cause of dropout and morbidity. PD Adequest software, which, through a mathematical model, predicts the effect of the dialysis prescription on the basis of the peritoneal transport, may be used to identify the noncompliant patient. Fifty patients from two dialysis centers, aged 65.9 +/- 1.5 years and on PD for 28.6 +/- 4.7 months, were studied. A peritoneal equilibration test (PET) was carried out and 24-hour urine and dialysate were collected. Total weekly creatinine clearance (CrCl, L/week/1.73 m2) was calculated, as well as the glomerular filtration rate (GFR), mL/min, mean CrCl and urea nitrogen clearance (UNCI). The dialytic schedules used were then introduced into the program and the parameters were recalculated using the software model. Nine patients considered noncompliant from their case histories were used to assess the differences of reference between expected and measured values. The control group was significantly different from the noncompliant group in the percentage of the CrCl and the serum creatinine (sCR) differences. The noncompliance threshold value was calculated from the mean of the lower 95% confidence interval of the compliant group and the higher one of the noncompliant group (-5.3%) for CrCl and vice versa for sCR (+10%), which behaved to the contrary. Reassessing the patients, 11 (22%) were identified as probably noncompliant.