An analysis of hepatic aflatoxin B1-DNA adduct (HADA) concentrations in rats and trout demonstrated that the hepatic cancer risk was linearly and quantitatively related in both species. Additionally, the adduct-risk correlation for short-term exposure accurately predicted chronic exposure risk in trout. Although rat and trout liver cells differ substantially in their nuclear DNA content, they appeared to experience similar cancer risks at a given HADA concentration. This may indicate that the liver nuclei of both species contain a similar number of an equivalent protooncogene(s). This analysis also provided a possible basis for the use of adduct measurements for estimating human cancer risk. The minimum human virtual safe dose for aflatoxin was estimated to be 0.264 ng/kg/day on the basis of this approach.