In vitro effects of hormonal stimuli upon tyrosinase and peroxidase activities in murine melanomas.

ACTH and corticosterone altered tyrosinase activity in the B-16, S-91 and Harding-Passey melanomas but did not evoke $\text{any}$ changes in peroxidase activity. Tyrosinase activity, but not peroxidase activity, was correlated with the degree of melanin pigmentation present in the melanomas. Thus, tyrosinase is the enzyme of physiological importance in the regulation of melanin pigmentation.