S: udies were made of serum macroamylase (large molecular amylase) detected in a patient of diabetes mellitus with hepatic disorders. Gel filtration and ultracentrifugation showed it to be in macromolecular (9 S) form. In acid dissociation (pH 3.4) it was separated into 7 S and of 4.5 S while undergoing perfect dissociat on in 6 M urea the amylase was of normal 4.5 S. When subjected to electrophoresis, this component moved as slow β, which suggested its loose combination with protein. No report may have been presented so far of such macroamylase as this case.