The present invention provides a method for increasing the activity of a mutant or wild-type .alpha.-glucosidase enzyme in vitro and in vivo by contacting the enzyme with a specific pharmacological chaperone which is a derivative of 1-deoxynojirimycin. The invention also provides a method for the treatment of Pompe disease by administration of chaperone small molecule compound which is a derivative of 1-deoxynojirimycin. The 1-deoxynojirimycin derivative is substituted at the N or C1 position. Combination therapy with replacement .alpha.-glucosidase gene or enzyme is also provided.