Changes in the secretory activity of two transplantable melanoma lines (differing in many biological features) as regards nitric oxide (NO) release and interleukin 6 (IL-6), tumor necrosis factor alpha (TNF-alpha) and oncostatin M (OSM) secretion were the subject of the present study. The results obtained show that a spontaneous alteration of the hamster native melanoma line into an amelanotic one is accompanied by a global change of the secretory activity, but there was not a distinct correlation between the endogenous cytokine secretion and NO secretion by cells of both melanoma lines.