Diabetes mellitus is a syndrome initially characterized by a loss of glucose homeostasis. The disease is progressive and is associated with high risk of atherosclerosis, kidney and nerve damage as well as blindness. Abnormalities in the regulation of peroxide and transition metal metabolism are postulated to result in establishment of the disease as well as its longer term complications. Diabetes mellitus is associated with oxidative reactions, particularly those which are catalyzed by decompartmentalized transition metals, but their causative significance in diabetic tissue damage remains to be established.