Abstract
The antitumor effect of methionine-enkephalin ([Met]enkephalin) was demonstrated in C57BL/6J mice inoculated with B16-BL6 melanoma cells. Local subcutaneous tumor growth was inhibited with a 50-μg dose daily for 7 or 14 days. The antitumor effect of [Met]enkephalin was inhibited by the administration of the opioid receptor antagonist naloxone. Naloxone alone had no significant effect on tumor growth.