Background : The present study was aimed at investigating the predictive parameters of erythropoietin (EPO) hyporesponsiveness in patients with continuous ambulatory peritoneal dialysis (CAPD). Methods : We studied 40 patients with end stage renal failure who were receiving peritoneal dialyis for at least 6 months and EPO therapy for at least more than 2 months. Pearson's simple correlation and multiple stepwise linear regression analysis was used to discover what parameter can predict EPO resistance. We expressed EPO resistance index (ERI) as 'weekly EPO dose/hematocrit/body weight'. The dose of EPO is titrated by about 25% every 2 or 4 weeks to maintain a target hematocrit between 33% and 36%. Results : We analyzed the relationship between ERI and other predictive parameters by Pearson's correlation. These results showed ERI has a statistically significant correlation with transferrin saturation (TS) (r=-0.327, p=0.042), total Kt/V (r=-0.423, p=0.018), serum albumin (r=-0.458, p=0.003), normalized protein catabolic rate (nPCR) (r=-0.479, p=0.006), normalized protein equivalent of total nitrogen appearance (nPNA) (r=-0.488, p=0.005) and serum C-reactive protein (CRP) (r=0.332, p=0.036). Regression analysis was performed using stepwise linear regression for multiple variables to discover the most independent variable which is correlated with ERI. ERI was entered as a dependent variable, whereas the other parameters (age, duration of peritoneal dialysis, serum albumin, CRP, serum ferritin, total Kt/V, nPCR, nPNA, serum iPTH, serum aluminium, TS) were entered as independent variables. This analysis showed CRP was the most significant variable, and if CRP is excluded, nPNA was the significant variable. CRP had a statistically significant correlation with serum albumin (r=-0.418, p=0.007) and total Kt/V (r=-0.366, p=0.043). High CRP group had more increased level of ERI(p<0.05), age(p<0.05) and serum creatinine(p<0.05) than normal control, but more decreased level of serum albumin(p<0.01) and serum iron level(p<0.05). Conclusion : These results indicate that CRP is the most important predictor of EPO hyporesponsiveness.(Korean J Med 59:183-191, 2000)