Cells of brewer’s yeasts Saccharomyces cerevisiae No. 1 were used as the experimental material. Cultivation was carried out in a BIOFLOW 3000 bioreactor (New Brunswick Sci.) using the YPD medium. Magnesium ions as MgCl₂·6H₂O were added at a dose of 1.25 g/L in two variants. In the first variant (Mg1), magnesium chloride was added to culture medium before the process of propagation had been initiated. In the second variant (Mg2), magnesium was added continuously to the culture medium during the first two hours of propagation. The supplementation of the culture medium with magnesium ions resulted in higher yields of biomass, compared to the control. Continuous dosing of magnesium was found to be better than a single-dose addition. Biomass obtained in the presence of magnesium ions contained more colony forming units than the control. Magnesium was absorbed by yeast cells and its level was twice as high as that measured in control experiments.