Bacterial infections and inflammation are among the ailments treated by traditional healers. The World Health Organization has expressed high interest in traditional medicine, and it is important to demonstrate scientifically that remedies employed in folk medicine are indeed therapeutically active. In this communication, antibacterial assays for 165 plant species conducted under simple laboratory conditions in a private clinic in Trujillo, Peru has been reported. The aim of the study was to scientifically test whether plants used in traditional medicine for the treatment of infections showed antibacterial activity. Extracts of samples of 148 species traditionally used as antibacterial were screened for activity against Staphylococcus aureus and Escherichia coli using an agar-diffusion method. In addition, 17 closely related species that were also part of the local pharmacopoeia, but only used for other purposes, were included for comparison. Sixteen species tested as traditional water extract and 96 species extracted in ethanol showed activity against at least one of the bacteria. The study confirms that simple laboratory methods are very well suited to assess the efficacy of traditionally used medicinal plants to inhibit bacterial growth. A comparison to the traditional uses also indicated that local knowledge can give important leads for the development of new treatments. Further tests, especially with regard to toxicity, are needed to verify the safety of the traditional preparations.