Isolated cell walls of bakers' yeast ( Saccharomyces cerevisiae, strain LK2G12) contain large amounts of invertase (β-fructosidase). Maltase (α-glucosidase) could not be detected in these preparations. Glucose and sucrose were fermented by cells grown on glucose, sucrose or maltose. Enzymic removal of the cell wall was paralleled by the release of soluble invertase and produced protoplasts which had lost the ability to ferment sucrose but not glucose. These protoplasts excreted substantial quantities of a soluble invertase during incubation with sucrose or glucose and the snail enzyme preparation. Maltose was fermented only by cells grown on this sugar. Protoplasts from these cells retained the ability to ferment maltose and released α-glucosidase upon lysis. Only small amounts of α-glucosidase were detectable in cells raised in a synthetic medium containing glucose as the only sugar. If the medium contained glucose or sucrose and low levels of maltose, the resulting cells did not ferment maltose nor did the derived protoplasts. Lysis of these protoplasts released substantial amounts of α-glucosidase. These results provide additional evidence that the major portion of the invertase is in the cell wall; in strain LK2G12 the rest is intracellular and not readily accessible to sucrose. Maltase is apparently only intracellular and becomes accessible to maltose through the action of an inducible system in the membrane.