The authors developed formulae calculating the daily drain volume (DV) required for a target normalized peritoneal clearance of urea (Kt/Vur) or creatinine (Ccr, Kt/Vcr) in peritoneal dialysis (PD). DV depends on the target clearance, the peritoneal solute transport type, and the size of the person as expressed by body surface area (BSA) or body water (V). To illustrate the formulae, we constructed nomograms for the following weekly target clearances: Ccr = 60 L/171.73 m2, Kt/Vur=2.0, Kt/Vcr=1.8 (the value corresponding to a Ccr of 60 L/1.73 m2 in a linear regression of the two parameters in 476 clearance studies in continuous ambulatory PD [CAPD] patients). The PD schedules studied included CAPD, continuous cycling PD (CCPD) with one 2 L daytime dwell, and a combination of daytime CAPD and nighttime automated PD (APD) with 2 hr dwell times. Peritoneal transport was characterized as low, low-average, high-average, or high by the dialysate-to-plasma (D/P) creatinine concentration ratio in a peritoneal equilibration test (PET). The D/P value entered for each transport type was the appropriate 95% lower confidence limit of the mean D/P in actual studies (2 hr and 4 hr D/P from 102 PET studies and 5.5 hr D/P from 476 clearance studies in CAPD patients). For high transport, the required DV values were similar in all three PD schedules studied. For low transport, the required DV was much larger, comparatively, for CCPD and CAPD-APD than for CAPD. Furthermore, the DV values required for a weekly Kt/Vur of 2.0 were comparatively less than the DV values required for a weekly Kt/Vcr of 1.8 (Ccr of 60 L/1.73 M2). Calculation of the DV required for different PD schedules, a target peritoneal clearance, and the patients's size is feasible when the patient's peritoneal transport characteristics are known. This calculation also allows the selection of the least costly PD schedule. Current target values for urea and creatinine clearance are incompatible in anuric PD patients.