Phenotype of lymphocytes was estimated in 16 peritoneal fluids obtained from 9 ovarian cancer patients. Peritoneal fluids contained predominantly T cells (more than 80%) while B cell content was relatively low. Approximately 50% lymphocytes carried T-helper cell marker (CD4). Percentage of T-cytotoxic/suppressor cells (CD8+ cells) differed between patients with progression and those showing no tumor progression (19.0 +/- 7.5 vs 32.7 +/- 18.5). CD4/CD8 ratio was higher in the group of patients with progression than in the group with no progression of the tumor (3.4 +/- 2.1 and 2.0 +/- 1.5). Chemotherapy did not affect the parameters. Estimation of CD8 and CD4/CD8 ratio in peritoneal fluid cells could be helpful in monitoring of disease progression.