An improved process for the production of glucose isomerase involves the addition of a specific amount of glycine (aminoacetic acid) to the fermentation medium. This increases the amount of the enzyme, glucose isomerase, that is produced by the microorganism, which preferably is a strain of Streptomyces, most preferably, S. olivochromogenes ATCC 21,114. Even further improvement is obtained by also adding a small amount of ammonium nitrate to the culture medium.