Tyrosinase activity, synthesis, mRNA, and its posttranslational processing were compared in hair follicular melanocytes of the C3HHeAvy mouse during eumelanogenesis and phaeomelanogenesis. Tyrosinase activity was increased during eumelanogenesis; this increase was accompanied by an increase in tyrosinase synthesis. Tyrosinase activity was also increased during phaeomelanogenesis, but only to a peak level that was 50% of that during eumelanogenesis. However, tyrosinase synthesis and mRNA levels were the same in follicles during eumelanin and phaeomelanin synthesis. The lower level of tyrosinase activity is, therefore, presumably due to posttranslational regulation. Less tyrosinase was associated with the particulate fraction during phaeomelanogenesis than during eumelanogenesis. Glycosylation of tyrosinase during phaeomelanogenesis was also reduced and may be the mechanism of control. Bromo-adenosine 3,5-cyclic monophosphate sodium salt increased glycosylation in both eumelanin and phaeomelanin, producing follicles; but this did not result in an increased uptake of tyrosinase onto the melanosome membrane. Therefore, although cAMP increased glycosylation of tyrosinase, the uptake of tyrosinase by the melanosome membrane appeared to be regulated by other systems that are limiting during phaeomelanogenesis, resulting in a lower level of tyrosinase activity.