Effects of dexamethasone on melanogenesis and tyrosinase mRNA levels were determined in B16/F10 melanoma cells. Melanin content of B16 cells increased in a dosedependent manner by the addition of dexamethasone to the culture medium. After 72 hr exposure, dexamethasone (10−6M) produced a 2.4‐fold increase in melanin content. Northern blot analysis revealed that tyrosinase mRNA level also increased by the addition of dexamethasone to the culture medium. After 24 hr exposure, dexamethasone (10−6M) caused a 1.8‐fold increase in tyrosinase mRNA levels. A tumor promoter, 12‐O‐tetradecanoyl phorbol‐13‐acetate (TPA) decreased tyrosinase mRNA level at 30 nM concentration. Dexamethasone antagonized this TPA mediated decrease in tyrosinase mRNA. It is suggested that glucocorticoids are involved in the regulation of tyrosinase activity at the transc