Some patients find automated peritoneal dialysis preferable to continuous ambulatory peritoneal dialysis (CAPD). Unfortunately, automated peritoneal dialysis prescriptions are time consuming and can impede rehabilitation. We wished to determine whether an 8-hour tidal peritoneal dialysis (TPD) prescription could maintain the time averaged blood urea nitrogen at 60 mg/dL or less while patients consumed a diet containing approximately 1.2 g protein/kg body weight/d. Ten home dialysis patients previously stabilized on continuous cyclic peritoneal dialysis volunteered for a metabolic balance study conducted at the University of Iowa's Clinical Research Center. A peritoneal equilibration test was conducted and mass transfer area coefficients (MTaCs) were derived for each subject. Nitrogen balance was measured during the last 5 days of a 12-day constant diet while patients underwent a series of monitored nocturnal dialyses. Mass transfer area coefficient measurements were reproducible and independent of the filling volume and ultrafiltration, but varied between subjects (normalized MTaCurea = 33.6 +/- 16.3 mL/min, normalized MTaCcrt = 16.3 +/- 9.5 mL/min). Tidal peritoneal dialysis urea and creatinine clearances could be predicted by these MTaC values (r2 = 0.70 urea, r2 = 0.91 creatinine). Nitrogen balance assumptions predicted, and we confirmed, a relationship between dietary protein intake and urea nitrogen generation (r2 = 0.82) during TPD. A normalized protein catabolic rate of 1.2 g/kg/d resulted in a urea nitrogen generation rate of approximately 100 mg/kg/d. If a patient's protein intake was approximately 1.2 g/kg/d, then TPD with a weekly urea clearance normalized to body volume (Kt/V(urea)) of approximately 2.1 (urea clearance, approximately 0.35 mL/kg/min) could maintain a time averaged blood urea nitrogen of approximately 60 mg/dL.(ABSTRACT TRUNCATED AT 250 WORDS)