Rabbit anti-tyrosinase antibodies were used to study the abundance, processing, and degradation of tyrosinase in murine (Cloudman) melanoma cells. The polyclonal antibodies precipitated low-molecular-weight (68,000 and 70,000) and high-molecular-weight (78,000 and 80,000) tyrosinases that had a precursor-product relationship. Cells with high basal tyrosinase activity had high levels of newly synthesized tyrosinase. Cells with low tyrosinase activity synthesized less tyrosinase and degraded the enzyme at a faster rate than cells with high tyrosinase activity. Melanotropin (melanocyte stimulating hormone), dibutyryl cyclic adenosine monophosphate, and isobutylmethylxanthine caused an increase in the abundance of newly synthesized tyrosinase that was directly proportional to the increase in enzyme activity. This enzyme was not a phosphoprotein. Other changes in the culture conditions that increased the level of tyrosinase activity increased the abundance of newly synthesized enzyme. It is thus concluded that the level of tyrosinase activity in Cloudman melanoma cells is a direct reflection of the abundance of enzyme protein.