ABSTRACTThe action of topically applied γ‐Oryzanol (triterpineol ester with ferulic acid) on the sebaceous glands was investigated using the double blind method. 1% γ‐Oryzanol ointment, and the ointment base as control, were applied symmetrically to the backs of rats in the same hair cycle stage. The turnover time of sebaceous gland cells was examined by quantitating8H‐thymidine incorporation and colchicine‐arrested mitosis.The labeling index and arrested mitosis values were significantly elevated by the topical application of γ‐Oryzanol. Elevation of these values was paralleled by an increase in sebum production (reported in a previous paper) (4), showing that sebaceous gland cells are stimulated by γ‐Oryzanol.Other than sex hormones, γ‐Oryzanol is the only substance known to stimulate sebaceous glands by t