In 248 strains representing 205 yeast species, changes in pH coupled to glucose addition were followed in unbuffered cell suspensions. Alkalinization of the external medium elicited by glucose, indicating a H+-glucose symport was observed in 34% of the strains, most of them belonging to the genera Rhodotorula, Hansenula and Candida. H+ uptake coupled to glucose transport was observed only after exhaustion of glucose in growth media. This observation was taken as an indication that, in general, the synthesis of H+-glucose symport is under the control of catabolite repression. Subsequently to the addition of glucose, in most yeasts (82%) acidification was observed. This ability is probably related to the creation of a proton-gradient across the plasma membrane and is generally distributed among yeasts.