Increased susceptibility to Rhizopus oryzae in diabetes was investigated using mice in which diabetic ketoacidosis was experimentally induced. All of the diabetic mice which had developed ketoacidosis died within four days after inoculation of R. oryzae and their serum UIBCs (Unbound iron binding capacity) were significantly lower than those of the normal control mice. This study suggested that the decreased serum UIBC produced by diabetic ketoacidosis enhances the growth of R. oryzae in vivo.