Acute skin damage and epithelial skin tumor formation were studied in albino rats exposed to graded doses of electrons having maximum ranges in skin of 0.36 mm, 0.75 mm, and 1.40 mm. Tumor formation and acute injury were found to Be highly dependent on the penetration of electrons for a wide range of surface doses. There is a critical depth in skin at 0.27 mm where the dose dependence of the tumor yield is independent of the penetration depth of the electron radiation.