Aromatic amines have long been recognized as animal and human carcinogens. Recently heterocyclic aromatic amines (thermic amines) have been found in small amounts in cooked foods, primarily meats, and have proven to be potent mutagens and rodent carcinogens. Availability of quantitative databases for mutagenic potency in Salmonella and for carcinogenic potency in rodents has made possible a study of ten heterocyclic thermic amines and 24 aromatic amines. Potencies on mutagenic and carcinogenic scales were significantly correlated. By multiple linear regression analysis and multivariate analysis of variance, two descriptive structural factors were found to modulate the two modes of biological response. These factors were number of rings and methyl substitution at carbon atoms. The quantitative correlation between mutagenic and carcinogenic potencies and the modulating structural factors suggest a significant similarity of molecular mechanisms and support the utility of the short-term bacterial assay in evaluating hazard levels.