Previous studies indicated that HC Blue 1 induced heptocellular carcinomas in B6C3F1 mice whereas the structurally similar nitroaromatic amine HC Blue 2 did not. In an attempt to elucidate the biochemical mechanisms responsible for their different carcinogenic potencies, comparative metabolism and genetic toxicity studies were undertaken. Eighteen-hour urinary recovery of administered radioactivity was equivalent for both compounds following oral gavage (100 mg/kg) in female B6C3F1 mice. By HPLC analysis, HC Blue 1 yielded 3 major polar metabolite peaks, one of which was susceptible to glucuronidase. In vivo metabolism of HC Blue 2 yielded a single major metabolite peak which was not hydrolyzed by glucuronidase. Metabolism by B6C3F1 mouse hepatocytes yielded metabolite profiles which were qualitatively similar to the profiles observed after in vivo metabolism. HC Blue 1 was metabolized by hepatocytes at approximately twice the rate of HC Blue 2. Cytogenetic evaluations of mouse hepatocytes after in vitro treatment indicated HC Blue 1 was more potent than HC Blue 2 in inducing chromosomal aberrations while both chemicals showed weak activity for inducing sister-chromatid exchanges. Furthermore, in the V79 cell metabolic cooperation assay, HC Blue 1, but not HC Blue 2, inhibited cell-to-cell communication suggesting a non-genotoxic activity may be present for HC Blue 1. It is concluded that qualitative and quantitative differences exist in the metabolism of these compounds and that genotoxic as well as nongenotoxic effects may contribute to their different carcinogenic potencies.