Several lysosomal glycosidase activities were examined in vitro during heat-induced germination of Dictyostelium discoideum spores and were found not to be coordinately controlled. The level of beta-glucosidase activity increased significantly during the emergence stage of germination. Both alpha-glucosidase and N-acetyl-beta-glucosaminidase activities remained relatively constant until postemergence, when they increased slightly; alpha-mannosidase activity decreased during all stages of germination. The activity of beta-galactosidase increased slightly during spore swelling, fell below the level initially found in spores at zero time, and increased slightly during postemergence. The expression of all of these enzyme activities, except the increase in beta-galactosidase, appeared to require protein synthesis. Spores in the lag phase of germination which were exposed to severe environmental stress were deactivated and exhibited reduced levels of alpha-glucosidase, beta-glucosidase, and N-acetyl-beta-glucosaminidase activities. Prolonged heat activation treatment reduced the levels of lysosomal glycosidase activities in postactivated spores but did not change the subsequent enzyme patterns during the spore-swelling and emergence stages of germination.