The carcinogenic potential of a technical-grade epoxy resin, Araldite GY 250, of which the diglycidyl ether of bisphenol A (DGEBPA) is the main component, was investigated in CF1 mice. Groups of 50 male and 50 female mice were treated for 2 yr by repeated epidermal application of a 1 or 10% (v/v) solution in acetone. The controls, 50 mice of each sex, were treated with acetone alone. The treatment had no effect on survival and no excess incidence of skin tumours occurred. A positive control group of 50 male and 50 female CF1 mice was treated by epidermal application of 2% (v/v) beta-propiolactone in acetone. In this group there was a high incidence of malignant skin tumours at the site of application and, consequently, increased mortality. Treatment with neither DGEBPA technical nor beta-propiolactone induced systemic neoplasia.