A new prenylated salicylic acid derivative, 3-farnesyl-2-hydroxy benzoic acid (1), was isolated from the leaves of Piper multiplinervium C. DC. (Piperaceae). It showed anti-Helicobacter pylori activity (MIC 37.5 mu g/ml) and antimicrobial activity at MICs between 2.5 and 5 mu g/ml against Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Mycobacterium smegmatis, Pseudonionas aeruginosa and Candida albicans. Its structure was elucidated by means of MS, H-1 and C-13 NMR. The ethnomedical claim of Piper multiplinervium to treat stomach aches by the Kuna Indians of Panama may be justified by anti-Helicobacter pylori activity of its MeOH extract. (c) 2005 Elsevier Ireland Ltd. All rights reserved.