It is generally accepted that residual renal function has significant meaning in dialysis adequacy of CAPD patients. However, the factors influencing the residual renal function have not been investigated yet. We evaluated the consequences of following factors on residual urine volume in 50 CAPD patients: deterioration rate of renal function (slope of I/serum creatinine) before dialysis, renal creatinine clearance at the initial point of dialysis and the episodes of rapid reduction of residual urine volume. There was no correlation between the deterioration rate of renal function before dialysis and the residual urine volume. On the contrary, there was significant correlation between renal creatinine clearance at the initial point of dialysis and the residual urine volume in the first 4 years on CAPD. We recognized 67 episodes of rapid reduction of residual urine volume after initiation of CAPD. Inappropriate management or complications attributed to the rapid urine volume reduction in 50 episodes. The residual urine volume did not recover to the previous level in 40 episodes. We concluded that early initiation of CAPD and evasion of decreasing residual urine volume caused by inappropriate management or complications have important meaning and will preserve residual renal function of CAPD patients.