The effects of topically applied spironolactone on the sebaceous glands of flank organs in adult male golden hamsters were investigated. Daily treatment with spironolactone (0.3 mg and 3 mg) on one side only significantly reduced the size of the treated flank organs, while the contralateral flank organs remained unchanged. Lower doses of spironolactone and the vehicle had no effect. Cyproterone acetate therapy resulted in the bilateral reduction of flank organ sizes. In vivo measurement of the palpable bulk of the flank organs correlated with flank organ volumes as determined by computer-assisted planimetry of serial histologic sections. Dry weights of seminal vesicles in animals treated with spironolactone did not differ significantly from those of the control group, while topically applied cyproterone acetate significantly reduced seminal vesicle weight. Topically administered spironolactone appears to have only local antiandrogenic effects, as indicated by the lack of changes in the untreated contralateral flank organs and in the weights of seminal vesicles.