Naturally occurring polysaccharides isolated from the yeasts are the substances with versatile intriguing biomodulatory activities. One of the novel derivatives prepared from the (1 ->> 3)-beta-D-glucan isolated from the cell walls of baker's yeast Saccharomyces cerevisiae is sulfoethyl glucan (SEG). Its DNA-protective, antimutagenic, anticlastogenic and cytotoxic/cytostatic enhancing effect was evaluated using five eukaryotic systems. SEG showed bioprotective effect in recombination- repair-deficient strain of alga Chlamydomonas reinhardtii against methyl methanesulfonate-induced genotoxicity, antimutagenic effect against ofloxacin-induced genetic changes in yeast Saccharomyces cerevisiae assay and anticlastogenic activity in plants Vicia sativa and Vicia faba assays against maleic hydrazide-induced clastogenicity. In the combined application with cytostatic drug vumon, SEG exerted enhancement of the drug's cytotoxic/cytostatic effect in the cell revitalization assay using mouse leukemia cells. The study sheds light on the possible mechanisms of actions and utilization of this microbial polysaccharide derivative in the cancer prevention and therapy.