Herbal medicine requires searching for new sources with antimicrobial activity. Alkanna sp. (Boraginaceae) is widely used in medicine due to detoxification and antibacterial effects. The aim of this study was to obtain Alkanna orientalis (L.) Boiss. plant callus extracts, to investigate antimicrobial activity of extracts against bacteria and yeast and to reveal responsible mechanisms. Callus tissue cultures have been obtained using different nutrient media. Antimicrobial activity and minimal inhibitory concentrations (MIC) were determined by the methods of extract diffusion in agar and dilution using different test-microorganisms. Quantity and quality of naphthoquinones were determined using spectrophotometric and high performance liquid chromatographic analyses. H ? /K ? exchange by whole cells was assayed using selective electrodes, ATPase activity and SH-groups number of membrane vesicles-by spectrophotometric methods. It was revealed that callus extracts containing naphthoquinones (0.19 ± 0.01 %) possessed bacteriostatic activity against gram-positive bacteria including pathogenic ones (MIC were 125-750 lg/mL -1 ), and bactericidal activity against lactic acid bacteria (Lactobacillus acidophilus, L. rhamnosus) (MIC was 250 lg/mL). MIC against Enterococcus hirae was 250 lg/mL of callus extract or 31.25 lg/ mL of shikonin. It depended on the medium content, cultivation duration and the activity remained for 10-11 years. Moreover, intact root extracts inhibited H ?