Flutamide (alpha,alpha,alpha-trifluoro-2-methyl-4'-nitro-m-propionotoluidide), at daily oral doses of 20 mg/day for 24 days, reduced the number and size of skin sebaceous gland cells, and reduced sebum production in ovariectomized, testosterone-stimulated rats. The weight of the preputial glands was also reduced. Unilateral topical application of flutamide (0.1-3.0 mg/day) to flank organs (androgen-sensitive cutaneous sebaceous structures) of testosterone propionate-treated female hamsters for 14 days resulted in bilateral reductions in flank organ weight and in inhibition of in vitro incorporation of 14-C from sodium [1--14C]acetate into lipids. Flutamide inhibition of flank organ weight paralleled the drug effect on lipogenesis. Unilateral topical application of flutamide to flank organs of intact male hamsters for 14 days resulted in significant bilateral reductions of flank organ weight at doses as low as 0.375 mg/day (the lowest dose tested). These weight changes were marked by reduction in sebaceous gland size, accompanied by focal cytoplasmic degeneration, and reductions in cytoplasmic organelles and in the size of the lipid bodies. Flutamide did not, however, seemingly alter the pattern of endogenous total lipids in sebaceous glands, nor did it alter the pattern of 14-C-incorporation into the lipids of male flank organ epidermis and isolated sebaceous glands, when compared to control, untreated preparations.