Density gradient centrifugation was applied to isolate cell subsets from tumor cyst and ascitic fluid in eight patients with ovarian serous carcinoma. A comparison of cellular composition and immunologic reactivity of cells from the cysts and from ascitic fluid in each patient was performed. Some differences in density profiles were found, but in each case the consistency of morphologic cell forms in the primary tumor and ascites was documented. Immunophenotypic analyses of isolated cellular fractions using polyclonal and monoclonal antibodies against ovarian carcinoma-associated antigens showed significant immunologic intratumoral heterogeneity. However, there was a similarity of antigen expression in cells from the primary tumors and ascitic fluids. Our study indicated that morphologic and antigenic characterization of a given tumor could be determined in a single representative sample of ascitic fluid.