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