The optimal way to objectively measure the adequacy of continuous ambulatory peritoneal dialysis (CAPD) therapy remains controversial. It has been suggested that one-third or more of all CAPD patients are presently receiving "inadequate dialysis" when dialysis prescriptions are not carefully calculated. To better define the therapy being delivered in a large, freestanding CAPD center, weekly KT/V urea and creatinine clearance per 1.73 m2 body surface area were measured in 56 of 180 patients randomly selected from our unit in whom dialysis prescriptions were arbitrarily determined by nurses and physicians. In addition, protein catabolic rates and selected clinical outcome criteria were assessed. Weekly KT/V urea correlated with weekly creatinine clearance (r = 0.50) as well as with the protein catabolic rate (r = 0.45). Patients were arbitrarily divided into three groups based on KT/V urea measurements. Thirty percent of the patients had weekly KT/Vs < or = 1.4, 41% had KT/Vs between 1.5 and 1.8, and 29% had weekly KT/Vs > or = 1.9. Significant differences were not noted in hospitalization rates, erythropoietin doses, or serum albumin concentrations in patients with KT/Vs < or = 1.4 and in patients with KT/Vs > or = 1.9. Peritonitis rates were highest in the patients with KT/V > or = 1.9. Therefore, in patients randomly selected from our large CAPD center, 30% of the patients had weekly KT/V urea measurements < or = 1.4. The clinical significance of this finding remains uncertain.