This study was undertaken to determine the magnesium ion biosorption ability of the C. utilis and S. cerevisiae yeast species during cultivation in model media supplemented with magnesium. The mannoprotein and b-glucan content in the investigated yeast cell wall were analyzed because of the essential function of yeast cell wall structural components in metal ion binding. At the same time, an observation of yeast cells with the use of a transmission electron microscopy (TEM) was performed. The S. cerevisiae No. 1 yeast demonstrated the largest magnesium cation biosorption capacity. The magnesium content in biomass of S. cerevisiae No. 1 was about 16 mg Mg 2? /g of dry substance after living cell incubation in MgSO 4 solution and about 18 mg Mg 2? /g of dry substance after pasteurized biomass incubation in YPD medium supplemented with magnesium ions. The tested yeast strains differed in mannoprotein and b-glucan content in the cell wall. The cell wall of S. cerevisiae 102, coming from YPD ? Mg 2? medium, contained the greatest amount of glycoproteins (approx. 66 % adjusted to a total sugar basis). The cell wall of C. utilis ATTC 9950 yeast incubated under the same conditions was composed mainly of b-glucans (approx. 78 %) with prevailing b-(1,6)-glucans in this glucose polymer fraction (approx. 53 %). In S. cerevisiae No. 1 and C. utilis yeasts, higher degrees of magnesium ion binding were observed in the presence of higher b-glucan content in the cell wall structure, whereas in S. cerevisiae, 102 cells the magnesium ion adsorption was determined mainly on the grounds of mannoprotein presence. The process of yeast cell pasteurization increased the magnesium ion binding ability in the tested fungi strains as a result of cell wall structure loosening. Introductory remarksYeast cells are, from the inside, enclosed with a cytoplasmatic membrane, periplasmatic space and cell wall successively. The yeast cell wall structure is mainly composed of polysaccharides of which content can constitute 20-90 % of this organelle dry substance [22,25,29,36]. Polysaccharides occurring in cell wall of the Saccharomyces genus are mainly b-glucans that make 30-60 % of cell wall dry substance [1,18,36].