We aimed to determine the mutagenic, antimutagenic and antigenotoxic effects of Rhizoplaca chrysoleuca and Rhizoplaca melanophthalma's methanol extracts on the known mutagens against two different organisms using mitotic index (MI) and Ames-Salmonella assay systems. For the MI assay the genotoxic dose of NaN3 was defined on Zea mays seeds and different dose of the lichen extract used as anti-mutagen (5, 10, 20, 40 mu g/plate). Observed data showed that methanol extracts prevent the cytotoxic effect of NaN3 partially. In addition, the antimutagenic activities of the methanol extracts were investigated against 9-AA in TA1537 and NaN3 in TA1535 strains of Salmonella typhimurium. Extracts show antimutagenic effect against 9-AA-induced mutation in TA1537 strain at all tested concentrations. The inhibition rates ranged from 70.73 to 85.71% (R. chrysoleuca, 0.5 mu g/plate - 5 mu g/plate). The results show that these natural compounds have an ability to reduce or prevent the effects of these mutagenic substances.