The pigment of human substantia nigra, neuromelanin, has been thought to be derived from dopamine. To examine the genesis of neuromelanin, we advanced a new hypothesis that neuromelanin is formed by oxidation of dopamine and cysteinyldopamine. On the basis of this hypothesis, synthetic neuromelanins were obtained by tyrosinase oxidation of dopamine in the presence of various ratios of cysteine and were hydrolyzed with hydriodic acid to obtain 4-amino-3-hydroxyphenylethylamine (AHPEA). The AHPEA content in these synthetic melanins was shown to be proportional to the sulfur content. Eleven samples of human substantia nigra were treated as well and contents of AHPEA were found to be only trace amounts. These results suggest that cysteinyldopamine may not be incorporated into neuromelanin.