The antimicrobial properties of protoanemonin isolated from the aerial parts of Ranunculus bulbosus were investigated. By its marked inhibitory effects and its broad spectrum of activity against aerobes and anaerobes including multiresistant pathogenic strains, protoanemonin could be considered as a promising antimicrobial natural compound. Combinations of protoanemonin and antibiotics were also investigated. Twenty two antibiotic-protoanemonin combinations against aerobic bacteria were studied: 20 combinations were partially synergistic (0.5<FIC⩽0.75) and in one case a total synergism (FIC⩽0.5) was observed. This striking result was obtained with the protoanemonin-cefamandole combination against a pathogenic strain of Staphylococcus aureus.