To investigate the factors affecting low values of serum albumin (SA) in continuous ambulatory peritoneal dialysis (CAPD) patients, we undertook a cross-sectional study of 106 CAPD patients, with a mean age of 49.0 years and dialysis duration of 43.4 months, with respect to demographic, clinical, and biochemical parameters. In group I (n = 28, SA < or = 3.5 g/dL), diabetics were more common, patients were significantly older, and more patients were malnourished, according to the subjective global assessment (SGA), compared to group II (n = 78, SA > 3.5 g/dL). Serum C-reactive protein (CRP), lipoprotein (a), and 24-hour dialysate-to-plasma creatinine concentration ratio (D/P) were significantly higher, and 24-hour dialysate albumin was greater in group I. Compared to group II, group I had significantly lower serum creatinine and urea nitrogen appearance (UNA). Blood urea nitrogen (BUN), lean body mass (LBM), % of body weight (%BW), and normalized protein equivalent of nitrogen appearance (nPNA) tended to be lower in the low SA group, without statistical significance. There were no differences in the duration of CAPD, peritonitis rate, serum insulin-like growth factor-I (IGF-I), anthropometric data, dietary assessment, dialysis adequacy, and residual renal function (RRF) between the two groups. SA was positively correlated with serum creatinine, IGF-I, LBM, UNA, BUN, nPNA, and CAPD duration, and was negatively correlated with 24-hour D/P, 24-hour dialysate albumin, age, CRP, and bicarbonate (HCO3-). By stepwise multiple logistic regression analysis, 24-hour D/P, age, CRP, and SGA were independent risk factors for low SA level. In conclusion, SA seems to be influenced not only by nutritional factors but also by nonnutritional factors such as peritoneal membrane transport characteristics, age, and presence of acute phase protein response manifested by CRP elevation.