The study concerns DNA ploidy and proliferative activity of the cells of two hamster transplantable melanoma lines - differing in many biological features - in the light of possible changes in their secretory activity. DNA ploidy was determined from the index of propidium iodide (PI) stained DNA content (DI), while the proliferative activity was defined as the percentage of cells in S and G2/M cell cycle phases. The secretory activity was described by determining total protein, interleukin 6 (IL-6), tumor necrosis factor alpha (TNF-alpha), oncostatin M (OSM), interleukin 10 (IL-10) and nitric oxide (NO) content in the supernatants after 1, 6, 24 and 48 hours in cell culture. Our results indicate that melanotic melanoma cells (Ma) have a near-tetraploid DNAcontent and about 18% of proliferating cells, while amelanotic melanoma cells (Ab) - have a near-triploid DNA content and almost twice as many proliferating cells. The Ab cells, in comparison with Ma cells, secreted in vitro less total protein and most of the cytokines examined except OSM, but a spontaneous alteration of transplantable melanoma was accompanied by an increase of the quantity and dynamics of NO secretion. So, the cells of two melanoma lines have their own characteristic pattern of secretory function. But, the aneuploidy which accompanied the changes in cell differentiation of the studied melanoma lines, although seemed to reflect their changes in the proliferative activity, nevertheless did not reflect, in a direct way, differences in the secretion of the substances studied.