Penetration of benzofajpyrene into the skin was measured in mice having unusual hair follicles or reduced numbers of hair follicles due to genetic mutation. Control animals consisted of sibling mice with a normal genetic background. The various mutant mice had large differences in the penetration of benzo[a]pyi'ene into their skin. Penetration was high in rhino and hairless skin, which had enlarged hair follicles with large sebaceous glands. Penetration was poor in ragged, o]X)ssum, and

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... skin, which had a reduced number of hair follicles. These results support previous observations that anatomic characteristics are principal factors that affect the jx-netration of hydrocarbons in skin. The findings also suggest the use of specific lines of mutant mice for ex|x>riments where either the surface epithelium or deeper cutaneous structures are to be selectively exposed to hydrocarbon carcinogens.