Biofilm embedded bacterial pathogens such as Staphylococcus spp., Escherichia coli, Pseudomonas aeruginosa, and Acinetobacter baumannii are difficult to eradicate and are major sources of bacterial infections. New drugs are needed to combat these pathogens. Hypericum is a plant genus that contains species known to have antimicrobial properties. However, the specific constituents responsible for the antimicrobial properties are not entirely known, nor have most compounds been tested as inhibitors of biofilm development. The investigation presented here tested seven secondary metabolites isolated from the species Hypericum densiflorum, Hypericum ellipticum, Hypericum prolificum, and Hypericum punctatum as inhibitors of bacterial growth and biofilm production. Assays were conducted against Staphylococcus epidermidis, Staphylococcus aureus, clinical methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa, Escherichia coli, and Acinetobacter baumannii. Five of the seven compounds demonstrated growth inhibition against the Gram-positive bacteria with minimum inhibitory concentrations (MIC) ranging from 1.95 µg/mL to 7.81 µg/mL. Four of the secondary metabolites inhibited biofilm production by certain Gram-positive strains at sub-MIC concentrations. Copyright © 2011 John Wiley & Sons, Ltd.