Twenty-seven ovarian cancer patients were observed for twenty-four months. The patients were grouped as follows: Group I-with complete (CR) or partial remission (PR), Group II-with stable disease (SD), Group III-with progression (PD) of the disease. In all patients, T lymphocyte phenotypes were estimated in peritoneal fluid (PF) and in peripheral blood (PB). No differences were observed in either PF and PBT (CD3+) cell percentages among the examined groups of patients. A slight increase was noted in the percentage of CD4+ cells upon transition from the remission group to the groups with less favourable outcome of treatment. The increase was observed both in PB and in PF but only the latter showed statistically significant changes. On the contrary, percentage of T-cytotoxic/suppressor (CD8+) lymphocytes decreased upon transition from patients with the remission to those with stable disease and those with progression. These changes strongly affected the CD4/CD8 ratio. In PF, CD4/CD8 ratios were 2.13 +/- 0.9 and 4.18 +/- 1.6 in Group II and III, respectively (p < 0.01). In PB, the ratios were 1.88 +/- 1.1, 1.75 +/- 0.6, and 4.32 +/- 1.5 in Groups I, II and III respectively (Group I vs. Group III p < 0.01, Group II vs. Group III p < 0.01). During the study, five patients died due to ovarian cancer. In retrospective analysis, these patients showed progressive increase in CD4/CD8 ratio of PFT cells. Just before death, the ratio demonstrated an abrupt increase. In conclusion, the estimation of CD4+ and CD8+ cells as well as calculation of CD4/CD8 ratio for lymphocytes of peripheral blood and peritoneal fluid seems helpful in monitoring disease progression in ovarian cancer patients.