Patients with advanced cancer have a depressed immunological function. We performed a battery of tests on peripheral blood samples from 42 patients with gynecological cancer to determine the extent to which this depression was due to abnormal lymphocyte function, as compared to changes in the number of lymphoid cells in the peripheral blood or in the efficiency of purification of cells in Ficoll:Hypaque gradients in preparation for testing. The percentage of lymphocytes in the gradient-derived cell suspension (% LG) and the absolute lymphocyte count were more informative than mitogen stimulation, mixed leukocyte culture, and T- and B-cell measurements. Both values decreased significantly with the advancing stage of cancer, and we were able to predict survival of patients with uniform stage of disease. The % LG correlated with survival better than did any other test when multivariate analyses of all test combinations were performed. Low values of % LG reflected both the depressed lymphocyte counts and the altered buoyant density of the leukocytes of many patients with advanced cancer. A large portion of the depression in other immune function tests was statistically attributed to changes in % LG and the lymphocyte counts. We concluded that these two simple measurements provide valuable information about patients with gynecological cancer.