Lipid-bound sialic acid (LSA) content and ganglioside composition in resected tumours and body fluids of patients with benign ovarian tumours, borderline ovarian tumours, ovarian cancer and also in unaltered ovaries of patients with uterine cancer were examined. LSA levels in tissues and relation of the main gangliosides GD3/GM3 progressively decreased from unaltered ovaries to ovarian cancer. Distribution of gangliosides GD3 and GM3 in the borderline tumours was not uniform. Absolute content of GD3 increased more than twice in profuse growth from the inner surface and decreased almost three times in the cyst capsule as compared to the intact tumour. Ganglioside GD3 content decreased in malignant ovarian tumours but increased in ascitic fluid of cancer patients as compared to GM3. These results suggest that ganglioside GD3 is shed more intensively in the borderline ovarian tumours.