Trehalose, a storage sugar of baker's yeast, is known not to be metabolized when added to a cell suspension in water or a growth medium and to support growth only after a lag of about 10 h. However, it was transported into cells by at least two transport systems, the uptake being active, with a pH optimum at 5.5. There was no stoicheiometry with the shift of protons into cells observed at high trehalose concentrations. Trehalose remained intact in cells and was not appreciably lost to a trehalose-free medium. The uptake systems were present directly after growth on glucose, then decayed with a half-life of about 25 min but could be reactivated by aerobic incubation with trehalose, maltose, alpha-methyl-D-glucoside, glucose or ethanol. The uptake systems thus induced were different as revealed by competition experiments. At least one of the systems for trehalose uptake showed cooperative kinetics. Comparative anaysis with other disaccharides indicated the existence in Saccharomyces cerevisiae, after induction with trehalose, of at least four systems for the uptake of alpha-methyl-D-glucoside, four systems for maltose, together with the two for trehalose, variously shared by the sugars, the total of alpha-glucoside-transporting systems being five.