Candida stellatoidea is classically distinguished from C. albicans by the ability of the latter species to assimilate sucrose. We show here that sucrose-positive revertants of C. stellatoidea type II are readily isolated and that C. stellatoidea type II strains probably resulted from a mutation in the sucrase gene of C. albicans. The revertants were not laboratory contaminants, as determined by restriction fragment length polymorphism analysis and retention of an auxotrophic marker. The reversion of three tested strains was accompanied by 16 to 110-fold increases in expression of a sucrase/alpha-glucosidase but not an invertase, with a Km for sucrose of about 1 mM. The enzyme activity was assayable in intact cells. The drastically increased expression of such an enzyme would allow extracellular sucrose hydrolysis and assimilation of the monosaccharide products.