Fabry disease is an X-linked lysosomal storage disorder caused by mutations in the gene encoding α-galactosidase A (α-Gal A), with consequent accumulation of its major glycosphingolipid substrate, globotriaosylceramide (GL-3). Over 500 Fabry mutations have been reported; approximately 60% are missense. The iminosugar 1-deoxygalactonojirimycin (DGJ, migalastat hydrochloride, AT1001) is a pharmacological chaperone that selectively binds α-Gal A, increasing physical stability, lysosomal trafficking, and cellular activity. To identify DGJ-responsive mutant forms of α-Gal A, the effect of DGJ incubation on α-Gal A levels was assessed in cultured lymphoblasts from males with Fabry disease representing 75 different missense mutations, one insertion, and one splice-site mutation. Baseline α-Gal A levels ranged from 0 to 52% of normal. Increases in α-Gal A levels (1.5- to 28-fold) after continuous DGJ incubation for 5 days were seen for 49 different missense mutant forms with varying EC50 values (820 nmol/L to >1 mmol/L). Amino acid substitutions in responsive forms were located throughout both structural domains of the enzyme. Half of the missense mutant forms associated with classic (early-onset) Fabry disease and a majority (90%) associated with later-onset Fabry disease were responsive. In cultured fibroblasts from males with Fabry disease, the responses to DGJ were comparable to those of lymphoblasts with the same mutation. Importantly, elevated GL-3 levels in responsive Fabry fibroblasts were reduced after DGJ incubation, indicating that increased mutant α-Gal A levels can reduce accumulated substrate. These data indicate that DGJ merits further evaluation as a treatment for patients with Fabry disease with various missense mutations.