In 44 patients with advanced ovarian carcinoma (OC) a fraction of CD45RO(+) lymphocytes in the blood and peritoneal carcinomatous fluid (PCF) was investigated. Thirty-one patients received cisplatinum with cyclophosphamide +/- doxorubicin. This group was followed from 2.2 to 9 years (mean: 45 months). In 23 out of 31 patients, the percentage of CD45RO(+) lymphocytes was higher in the PCF than in the blood samples. Patients with these higher lymphocyte levels experienced longer survival than those who did not show any excess of CD45RO(+) lymphocytes in PCF ( P=0.02). This was further verified by the use multivariate Cox analysis which included an assessment of the percentage of CD45RO(+) lymphocytes in PCF, age, FIGO status, histology, treatment (CAP or CP) and residual disease (RD) post-surgery. This analysis revealed that two factors had an independent power of prediction: RD ( P=0.02) and the percentage of CD45RO(+) cells in PCF ( P=0.04). Therefore, CD45RO(+) lymphocytes were studied in further detail in a group of 20 patients. This study revealed that PCF CD45RO(+) lymphocytes were characterized by: (1) a higher proportion of cells co-expressing activation markers (HLA-DR, CD28) and higher levels of mRNA for CXC chemokines (IP-10, IL-8) and for IL-10, but with lower levels for IL-2; (2) higher levels of Ki67, bcl-2 and p53 mRNA as compared to those in blood. In conclusion, in the present study it was found that an accumulation of activated CD45RO(+) cells in PCF had a beneficial effect on the survival of patients receiving platinum-based chemotherapy.