Malignant and non-malignant serosal fluids were found to be associated with high serum levels of CA-125, suggesting that the presence of fluid in the serosal cavities may stimulate its release. In this study, we investigated the relationship between serum CA-125 levels and peritoneal irritation during continuous ambulatory peritoneal dialysis (CAPD). We performed a clinical study in 24 stable patients (15 amenstrual females and 9 males), aged 46 ± 14 years on CAPD. The control group consisted of 32 healthy volun­teers (20 females, 12 males) aged 44 ± 12 years. CA-125 levels were determined prior to the CAPD dwell (without dialysate in abdomen) and during the CAPD dwell (dialysate in abdomen 4 hours after). As a result, serum CA-125 levels were found to be 14.86 ± 5.98 U/ml and 15.23 ± 6.05 U/ml respectively, whereas it was 8.32 ± 5.54 U/ml in the control group. Serum CA-125 levels were found to be significantly elevated in CAPD patients when compared with healthy volunteers. However, serum CA-125 levels detected prior to and after CAPD did not differ between the groups. Interestingly, all of the patients in our study group were detec­ted to have normal serum CA-125 levels (<35 U/ml). We concluded that CAPD-induced abdominal artificial ascites did not affect serum levels of CA-125. Moreover, short and non-inflammatory mechanical pressures in the CAPD procedure do not have any effect on serum CA-125 levels.