Two strains of mice, CF‐LP and Swiss‐Webster random‐bred, were evaluated for liver neoplasia after administration of oral contraceptive steroids. No increased incidence of hepatocellular tumors was found beyond the variation expected by chance. The overall tumor incidence in treated and untreated groups was identical. No significant increase in tumor size was observed in the treated animals. Liver weights progressively increased in several of the treated groups. In both treated and untreated animals hepatocellular neoplasia was usually accompanied by intracytoplasmic inclusions similar to those observed in human liver tumors. Vascular lesions were observed in some of the animals receiving large doses of contraceptive steroids. While these may be the result of local toxicity, their similarity to lesions observed in benign liver tumors warrants further investigation. No evidence was found to suggest that contraceptive steroids act as initiators of liver neoplasia.