Dyes based on known carcinogens such as benzidine and beta-naphthylamine can no longer be manufactured in the United States. In addition, numerous colorants have been banned from use by the food and cosmetic industries. These limitations have led to the examination of structure-activity relationships that could help in the development of suitable nongenotoxic dyes and dye precursors. The authors' goal was to demonstrate how nonmutagenic dyes could be developed by identifying nongenotoxic dyestuff intermediates. The authors' working hypothesis stated that an azo dye would be nonmutagenic if both the synthetic precursors and reductive cleavage products of the dye were nonmutagenic themselves. By examining a related series of compounds, the work was able to demonstrate the effect of adding specific substructural components to parent compounds used in the synthesis of dyes. The paper provides an overview of these structure-activity studies.