Three lichen depsidones, physodalic acid (1), physodic acid (2), and 3-hydroxy physodic acid (3), were isolated from Hypogymnia physodes diethyl ether extract using column chromatography, and their structures determined by comparing their UV, H-1 and C-13 NMR spectroscopic and MS data with those given in the literature, as well as with data computed by CHEM draw ultra 11 software. The contents of 1, 2 and 3 were determined in the methanol (ME), acetone (AE), and diethyl ether (EE) extracts using reversed-phase high performance liquid chromatography with photodiode array detection. The extracts, isolated depsidones 1-3 and EE fraction F23 (consisting of 90% 2 and 3, in the ratio 5.5: 1) were evaluated for their in vitro effects on chromosome aberrations in peripheral human lymphocytes using the cytochalasin-B blocked micronucleus (CBMN) assay in doses of 1 mu g/mL and 2 mu g/mL of final culture solution. The frequency of MN was scored in binucleated cells, and nuclear proliferation inde...x was calculated. It was found that 1, 2, 3, F23, and EE at 1.0 mu g/mL exerted a beneficial effect on lymphocyte cells giving a significant decrease of the frequency of MN in comparison with the positive control Amifostin WR-2721. Among the tested depsidones at a concentration of 1 mu g/mL, 3 exhibited the most prominent effect decreasing the frequency of MN by 30.3%, followed by 2 (28.2%) and 1 (22.0%). The extracts were less effective than the isolated depsidones.