The reactions between aminochromes and thiols have been reinvestigated. In general aminochromes react with thiols to give mixtures of products including: 5,6-dihydroxyindoles; thio-substituted 5,6-dill>-droxyindoles (the mercapto residue is no\\ considered to be in the 4-position of the indole nucleus and not the 7-position as previously reported); and relatively unstable addition products formed between the aminochronie and the thiol. The mechanisms by which these conlpounds are formed are discussed. The characterization of three thio-substituted 5,6-dihydroxyindoles by nuclear magnetic resonance spectroscopy is described. The nuclear magnetic resonance spectra of a number of 5,6-diacetoxyindole derivat~vcs are reported.