Sugar uptake is accompanied with H^+ -substrate-symport generally. Both H^+ /sugar-and H^+/K^+ stoichiometries during the sugar-uptake have been reported to be exactly 1 : 1. This paper reports that the stoichiometries were enhanced dramatically by the addition of CaCl_2 into the medium and by the high cell density of 200 ㎕ pc/mL. The concentration of free Ca^2+ ions in the cells increased significantly with cell densiy. It is suggested that the free Ca^2+ ions are responsible for the change of stoichiometry of sugar transport system by regulation of H^+ ion level of biomembrane.