Hamster melanoma cells (RPMI 3460) were examined for their ability to utilize phenylalanine for melanin biosynthesis. There was a small but significant incorporation of L-[1-1414C] phenylalanine into hot acid-insoluble cellular material in the presence of cycloheximide. However, this radioactivity was removable from the acid-insoluble fraction by pronase digestion. A similar percentage of L-[U-14C] leucine incorporation was likewise resistant to cycloheximide inhibition. Residual protein synthesis is apparently responsible for the incorporation of both amino acids. Cycloheximide did not inhibit melanin synthesis. These results suggest that mammalian melanocytes do not use phenylalanine for melanin synthesis. Phenylalanine is not incorporated directly into melanin, nor do the cells appear to convert it to tyrosine via a phenylalanine hydroxylase.