In algae possessing lichens, polyols serve as energy-storing compounds. They are also osmotically-active compounds that increase lichen resistance to low and freezing temperatures. Natural levels of polyols in lichens are species-specific. They vary within 1.4-8.8 mg.g-1 DW (ribitol), 0.4-29.0 mg.g-1 (mannitol). We investigated natural and experimentally-affected contents of polyols and non-structural saccharides (NSS). Ribitol, mannitol, arabitol and NSS were HPLC-evaluated before and after the experimental treatments: in-vitro exposition of thalli to additional ribitol (32, 50 mM for 168 h at +5, 0, -5 deg C). Initial values were 2.6, 4.1 mg.g-1 DW (ribitol, mannitol). Addition of ribitol led to increased levels of mannitol (at all temperatures), while ribitol, arabitol and fructose showed either no or insignificant change. In control and ribitol-treated lichens, lowest mannitol content was found at -5 deg C. The results were attibuted to altered utilization of polyols at freezing temperature. Underlaying mechanisms of low temperature-dependent changes in polyol exploitation are important for the lichen life strategy at low and freezing temperatures. The abstract was supported by the KJB601630808 project funded by the Grant Agency of the Czech Academy of Science (GAAV), Czech Republic.