Cytotoxic and genotoxic effect of (+) and (–) enantiomers of usnic acid in human peripheral blood lymphocytes studed. We have shown that the studied usnic acid enantiomers in concentrations of 0.04—0.30 mM have a pronounced cytotoxic effect. We have found that the enantiomers of usnic acid in concentrations 0.04—0.30 mM exhibit genotoxic effect. Genotoxicity of (–)-usnic acid enantiomer in concentrations of 0.15 and 0.30 mM was in 2 times higher than hat of the (+) enantiomer. It has been noted that (+) and (–) usnic acid enantiomers induce atypical «comets» (hedgehogs). Wherein, (–)-usnic acid induced to 2.5—3.5 times more atypical «comets» than its (+) enantiomer.