The present invention provides a method for increasing the activity of amutant or wild-type .alpha.-glucosidase enzyme in vitro and in vivo bycontacting the enzyme with a specific pharmacological chaperone which is aderivative of 1-deoxynojirimycin. The invention also provides a method for thetreatment of Pompe disease by administration of chaperone small moleculecompound which is a derivative of 1-deoxynojirimycin. The 1-deoxynojirimycinderivative is substituted at the N or Cl position. Combination therapy withreplacement .alpha.-glucosidase gene or enzyme is also provided.
