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Antonios H. Tzamaloukas, Renal Section (111C), VA Medical Center, 2100 Ridgecrest Dr, SE, Albuquerque, NM 87108 (USA) Dear Sir, Plasma concentrations of creatinine greater than 1,600 μmol/l (18 mg/dl) and urea greater than 35 mmol/l (BUN > IOO mg/dl) were proposed as indicators of inadequate peritoneal dialysis [1, 2]. However, the range of plasma concentrations of these two substances is almost identical in CAPD patients with clinical manifestations of inadequate dialysis and those adequately dialyzed clinically [3]. Thus, the use of plasma creatinine or urea concentration to assess the adequacy of peritoneal dialysis is, in general, questionable [3]. We report two cases illustrating the circumstances under which plasma creatinine is a strong indicator of peritoneal dialysis inadequacy. Both patients were men on CAPD. Renal failure was caused by hypertensive nephro-sclerosis and idiopathic proliferative glomer-ulonephritis. Age at onset of CAPD was 39 and 43 years, respectively. The first patient has had no peritonitis or exit site infection. The second patient had an exit site infection 7 months before the first clearance study and lost his peritoneal catheter to Candida para-psilosis peritonitis 6 months after the last clearance study. A few months after the first study both patients noticed progressive decrease in daily urinary volume followed within 2-4 months by anorexia, decreased food intake and occasional vomiting. In addition, the first patient developed severe hypertension, which responded to increasing doses of antihypertensive agents only after reduction of body weight by 3 kg. The second patient developed progressive neuropathy and impotence. Sequential 24-hour fractional clearance of urea and creatinine clearance studies were performed. Instilled dialy-sate volumes did not change, at 10 1/day, between the first and second study in both patients. However, while the clearance indices were in the adequate range (weekly fractional clearance of urea > 1.70, weekly creatinine clearance > 50 1/1.73 m2) in the first study, the second study produced inadequate clearance indices, primarily because of loss of urinary clearance. After the second study, instillation volume was increased to 16 liters daily in both patients. The first patient reported complete disappearance of the symptoms, while uremic symptoms persisted in the second patient. Instillation volume was further increased to 22 liters daily in the second patient with disappearance of anorexia and nausea and improvement of neuropathy. Weekly total (dialysate plus urine) fractional clearance of urea and creatinine clearance were computed according to the method of Nolph et al. [4]. Glucose concentration (Gl) in the