d-Gluconamide, d-gluconyl hydrazide, and N-(6-aminohexyl)- d-gluconamide were prepared from d-glucono-1,5-lactone by treatment with ammonia, hydrazine, and 1,6-diaminohexane, respectively. These d-gluconamide derivatives were tested for their inhibitory action on human liver lysosomal glucocerebrosidase and human spleen neutral aryl β-glucosidase. Analogous d-galactonamide derivatives were evaluated for their inhibition of human spleen galactocerebrosidase and G M1-ganglioside β-galactosidase. d-Gluconyl hydrazide and d-gluconamide were effective inhibitors of the lysosomal glucocerebrosidase, attaining 50% inhibition at 5 and 12 m m, respectively. In contrast, N-(6-aminohexyl)- d-gluconamide did not inhibit the glucocerebrosidase. d-Gluconyl hydrazide was also the most effective inhibitor of human liver and spleen aryl β-glucosidase, 50% inhibition being achieved at 4 m m concentration (competitive inhibition, K i = 0.4–0.9 mM). d-Galactonamide was the most effective inhibitor of spleen galactocerebrosidase; 4 m m d-galactonamide caused 50% inhibition of the enzyme activity (noncompetitive inhibition). N-(6-Aminohexyl)- d-galactonamide is a potent inhibitor (90% inhibition, 5 m m) of G M1-ganglioside β-galactosidase but is without effect on galactocerebrosidase. It has, therefore, the potential usefulness in distinguishing between two of the galactosphingolipid β-galactosidases.