Sudan 1 was associated with a significant increase in neoplastic nodules and carcinomas in, both male and female rats. Under conditions of other studies, no significantly increased incidence of micro-nucleated hepatocytes were found after the administration of Sudan 1. These results suggest that the liver carcinogenicity may not be due to the genotoxic effects of Sudan 1. No carcinogenic effects were visible in livers of mice after the application of Sudan 1. But when Sudan 1 is applied subcutaneously to mice, liver tumors were found.