Existing methods for the histochemical demonstration of liver phosphorylase activity were investigated for possible application to a study of enzyme activity using the electron microscope as well as the light microscope. It was found that lead, in concentrations recommended in the literature, cannot be used as the precipitating agent because of its inhibitory effect on phosphorylase activity. The histochemical method based on the demonstration of enzymatically formed glycogen can be improved by adding ethylenediaminetetraacetic acid to the incubating solution. However, the addition of 3',5'-cyclic adenosine monophosphate is not as effective. It is not necessary to add glycogen to the incubating solution. In our opinion enzyme activity cannot yet be demonstrated electron microscopically by the precipitation of liberated phosphate. This is due to the inhibitory effect of high lead concentrations. Under the light microscope the method based on the demonstration of enzymatically formed glycogen is most reliable.