To the Editor.—Ìý I observed with interest the scientific exhibit on cycloheximide at the 1978 Academy of Dermatology meeting in San Francisco.¹ A simple in vivo assay was demonstrated for this new topical epidermal cytotoxic drug for the treatment of epithelial neoplasms. Du Vivier showed that cycloheximide, applied topically, is a potent local inhibitor of epidermal cell division. Histologically proved basal cell carcinomas and actinic keratoses were treated.I would like to report that I have used cycloheximide in a concentration of 0.025% in an absorbent ointment base (Aquaphor) on six patients for extensive advanced actinic keratosis of the face and chest. Three of these adult patients were allergic to the compound fluorouracil, confirmed by patch testing.I have observed that cycloheximide produces a brisk inflammatory reaction that reaches a peak somewhere between eight to 14 days after initial treatment. The inflammation occurs more rapidly than the inflammation