The use of strontium 90 has proved to be efficient and practical, because handy, and permitting short treatment, not only, to cure benign superficial tumors and, as reported in this study, of pre-cancerous lesions such as actinic keratosis, Bowen's disease of the skin but also some carefully chosen cases of superficial carcinomas. Hundred lesions have been so treated and followed for 3 years; two only have relapsed. The cosmetic result has been excellent in 80 p. 100.