Results from a dose-response study in rats are reported, in which daily oral doses of 10, 3, 1, and 0.3 mg/kg bodyweight/day respectively were administered. The three highest dose levels resulted in incidences of liver cancer of 46, 84, and 32% respectively. In the lowest dose group (0.3 mg/kg/day) no statistically significant increase in tumor rate compared to untreated controls was found.