4-Vinyl-1-cyclohexene diepoxide (VCHD) is used as a chemical intermediate and as a reactive diluent for diepoxides and epoxy resins. Studies were conducted by administering VCHD in acetone by dermal application, 5 days per week for 105 weeks, to groups of 60 rats of each sex at 0, 15, or 30 mg/animal. Groups of 60 mice of each sex were administered 0, 2.5, 5, or 10 mg/animal on the same schedule for up to 103 weeks. Ten animals from each group were humanely killed, necropsied, and examined histopathologically during Month 15. At the 15-month evaluation, 2 of 10 male rats that received 30 mg had a squamous cell carcinoma of the skin at or adjacent to the site of application. Squamous cell papillomas and carcinomas were seen in all mice that received 5 or 10 mg. Two of nine female mice given 10 mg had granulosa cell tumors of the ovary, and one of nine female mice given 10 mg had an ovarian papillary cystadenoma. In the 2-year studies, body weight and survival were lower in high-dose rats and mid- and high-dose mice than in vehicle controls. All high-dose male mice died by Week 83; remaining high-dose female mice were killed during Week 84 for humane reasons. Squamous cell papillomas of the skin in dermally exposed male rats and squamous cell carcinomas and basal cell adenomas or carcinomas of the skin in exposed male and female rats were increased. The incidence of squamous cell carcinomas of the skin was increased in male and female mice at all dose levels. Mid- and high-dose female mice had an increased incidence of benign or malignant granulosa cell tumors and of benign mixed tumors of the ovary.