Extracts of tea (Camellia sinensis) can reverse methicillin resistance in methicillin-resistant Staphylococcus aureus (MRSA) and also, to some extent, penicillin resistance in beta-lactamase-producing S. aureus. These phenomena are explained by prevention of PBP2' synthesis and inhibition of secretion of beta-lactamase, respectively. Synergy between beta-lactams and tea extracts were demonstrated by disc diffusion, chequerboard titration and growth curves. Partition chromatography of an extract of green tea on Sephadex LH-20 yielded several fractions, one of which contained a virtually pure compound that showed the above-mentioned activities, at concentrations above about 2 mg/L. The observed activities are novel and distinct from the previously reported direct antibacterial activity of tea extracts. Prevention of PBP2' synthesis offers an interesting possible new approach for the treatment of infections caused by MRSA.