The cells of tumor fluid from patients with malignant and benign serous ovarian neoplasms were fractionated using Ficoll-Uropoline density gradient centrifugation. Density distribution and morphologic characteristics of cell fractions were analyzed. It was found that serous ovarian adenocarcinomas contained three to four types of morphologically malignant cells focused in low density layers. Borderline ovarian neoplasms showed the presence of one subpopulation of cells with some features of malignancy and cells with some atypical but non-malignant features. The fluids of serous cysts contained mainly normal epithelial cells representing different stages of morphological maturity and were focused in denser layers. The results allowed us to catalogue ovarian tumor cell subpopulations present in each density fraction of individual patients and confirmed that ovarian tumors could be diagnosed by morphologic identification of cells from tumor fluids.