beta-Glycyrrhetinic acid isolated from Glycyrrhiza glabra had an antibacterial activity of 7.6 and 12.5 mug ml(-1) against Bacillus subtilis and Staphylococcus epidermidis without causing hemolysis of human erythrocytes, whereas it was not inhibitory against Escherichia coli, Proteus vulgaris and various fungi. Confocal microscopy showed that beta-glycyrrhetinic acid was located within the bacteria but had not caused membrane disruption. It then inhibited synthesis of DNA, RNA and protein.