The properties of glucose isomerase in native, heat-treated and immobilized cells of Streptomyces kanamyceticus after heat and mineral treatment have been compared. The optimum pH for glucose isomerase in native cells was shifted from 8.2 to 8.6 by heat treatment and immobilization. There is no change in the optimum temperature (90 degrees C) for activity of the enzyme by the above treatment. Heat-treated cells and immobilized cells show greater pH and thermal stability of the enzyme. The Km values of the enzyme of native cells, heat-treated cells and immobilized heat-mineral-treated cells are 208 mM, 212 mM and 166 mM respectively; Mg++ and Co++ enhance the activity of isomerase in all cases.