This report concerns a study of the effect of ethanol and acetaldehyde on the regulatory enzymes of glycogen metabolism. It demonstrates an inhibition of glycogen phosphorylase kinase at pH 6.8 at a very low concentration of ethanol. There was no effect of acetaldehyde on this enzyme. Neither ethanol not acetaldehyde has been shown to have any effect on glycogen synthase, glycogen phosphorylase, protein phosphatase or independent and cAMP-dependent protein kinases. This inhibition could explain the high concentration of glycogen in the muscle tissue of chronic alcoholics that is found when ethanol is present in skeletal muscle.