GLUCOSE dehydrogenase from spores of Bacillus cereus is heat stable in solutions of sodium chloride at pH 6.5 (ref. 1). Increasing concentrations of sodium chloride also protect the enzyme from inactivation by 8 M urea. The enzyme has a half-life of 7 min in 8 M urea, pH 6.5, but in 8 M urea : 1 M solutions of sodium chloride, the half-life of the enzyme is 192 min. The rate of decay of glucose dehydrogenase activity in the presence of urea follows second order kinetics2. A number of enzymes can be protected from urea inactivation by their specific substrates3–8. In this communication we report the effect of glucose in stabilizing glucose dehydrogenase and partially reversing the inactivation resulting from urea.