Dialysis adequacy has a major impact on outcome of continuous ambulatory peritoneal dialysis (CAPD) patients. However, there is a substantial confounding effect by residual renal function in most studies. We differentiated the effects of dialysis adequacy from those of residual renal function on nutritional status and outcome of CAPD patients. We identified 168 CAPD patients treated in our center between September 1995 and December 1996 and categorized them into three groups: 49 patients with an average total Kt/V of 1.93 +/- 0.18 and a median residual glomerular filtration rate (GFR) of 0. 07 mL/min/1.73 m(2) in the dialysis-dependent (DD) group; 48 patients with an average total Kt/V of 2.03 +/- 0.25 and a residual GFR of 2. 33 mL/min/1.73 m(2) in the residual renal function (RRF) group; and 71 patients with an average total Kt/V of 1.38 +/- 0.22 and a residual GFR of 0.05 mL/min/1.73 m(2) in the control (CTL) group. They were followed-up for 1 year to compare baseline nutritional status and 1-year morbidity. Baseline normalized protein catabolic rates (NPCR) are 1.00 +/- 0.20 and 0.96 +/- 0.19 (for RRF and DD, respectively) versus 0.89 +/- 0.16 g/kg/d for CTL (P < 0.01). Percentage lean body mass (%LBM) was 71.6 +/- 9.8 and 71.5 +/- 10.0 (for RRF and DD, respectively) versus 65.2 +/- 8.5% for CTL (P < 0. 001). No difference was seen in the nutritional status between RRF and DD groups. Duration of hospitalization for 1 year was 6.9 +/- 11. 8 days in the RRF group versus 14.9 +/- 25.1 in the DD and 10.6 +/- 11.6 days in the CTL groups (P < 0.05). The peritonitis rate was 44. 4 patient-months for the RRF group, versus 13.6 for the DD and 12.9 for the CTL groups (P < 0.05). There also was a trend toward superior 1-year technique survival in the RRF group, but the number of observations was small. There was no difference in duration of hospitalization, peritonitis rate, and technique survival between the DD and CTL groups. Short-term morbidity in patients without residual renal function appears to be independent of total Kt/V, although Kt/V may have some effects on nutritional status. The assumption that renal and peritoneal clearances are equivalent must be carefully reexamined. Further studies on the effect of dialysis adequacy in patients without residual renal function are urgently needed.