Zinc displays 'in vitro' some antiandrogen activity through an inhibition of the 5 alpha-reductase activity. The clinical relevance of this effect is unknown, particularly during zinc therapy of acne. As sebum production could be a pharmacological target, a sensitive method was used for measuring the rate of sebum delivery to the skin surface during treatment with a topical 4% erythromycin-1.2% zinc acetate formulation. A series of four successive 1-h samplings with Sebutape was taken to derive the rate of sebum output from the slope of the regression line given by cumulative data. As a control the classical photometric method was used. Such combined evaluation revealed a sebosuppressive effect for the topical zinc formulation tested.