The main volatile compounds from three medicinal plants belonging to Lamiaceae family were screened for their biological properties. The plants were Salvia officinalis, Thymus vulgaris, and Mentha × piperita containing as the main volatile constituents thujone, thymol, and menthol, respectively. The applied chromatographic system was silica gel developed with toluene-ethyl acetate (93:7). Thin-layer chromatography — direct bioautography (TLC-DB) against Escherichia coli and Bacillus subtilis was used for detection of antibacterial activity of the plant extracts and essential oils. The bioautographic fingerprints were compared with the fingerprints obtained after derivatization with anisaldehyde.