AbstractThe influence of selenium dioxide on thein vitroandin vivogrowth of transplantable B16 melanoma was studied. In thein vivostudy, melanoma tissues showed a decrease in development of tumor growth and a tendency toward higher levels of free radical signal (ESR). Cultured B16 melanoma cells revealed a marked disturbance of cell growth especially in the solution with a high dose of selenium.These results may indicate that selenium has an antitumorigenic effect on B16 melanoma cells.