The use of creatinine clearance for adequacy of continuous ambulatory peritoneal dialysis (CAPD) requires consideration of the fact that a significant fraction of residual renal creatinine clearance is contributed by tubular secretion. We analyzed 123 peritoneal dialysis (PD) patients and corrected the residual renal creatinine clearance by averaging renal creatinine and urea clearance to estimate the glomerular filtration rate (GFR). Modified total creatinine clearance (peritoneal plus estimated renal GFR) was compared with total creatinine clearance (peritoneal plus total renal creatinine clearance). Modified and total creatinine clearances were not significantly different in patients with a total creatinine clearance less than 60 L/week/1.73 m2 body surface area (BSA), but a significantly lower modified total creatinine clearance was seen with patients having greater than 60 L/week/1.73 m2 BSA of total creatinine clearance. The correlation was better between KT/V and modified total creatinine clearance (r = 0.74) as compared to KT/V and total creatinine clearance (r = 0.67). We suggest that if creatinine clearance is used for peritoneal dialysis (PD) adequacy, the contribution of residual renal function should be calculated as the average of renal creatinine and urea clearance, thus estimating creatinine clearance only by the GFR. Further long-term studies are needed to confirm that modification of total creatinine clearance will better predict clinical outcome.