The crude extract of Mahonia aquifolium (Pursh) Nutt. stem bark and its two main protoberberine alkaloids, berberine and jatrorrhizine, were tested for their in vitro antimicrobial activity. Twenty strains of coagulase-negative staphylococci and 20 strains of Propionibacterium acnes isolated from skin lesions of patients with a severe form of acne, and 20 strains of Candida sp. isolated from chronic vulvovaginal candidoses were tested for their susceptibility to crude extract and two isolated alkaloids. The minimum inhibitory concentrations obtained in this study illustrate the varying degrees of antibacterial and antifungal activity of the tested agents. The results indicate a rational basis for the traditional use of Mahonia aquifolium for localized skin and mucosal infection therapy, as well as for the possible development of a preparation for supportive therapy of the diseases mentioned above.