The changing definition of diabetes, brought up to date, includes the concepts of premellitus as well as mellitus, and of an enzymatically impaired or otherwise ineffective insulin as the possible cause of the full syndrome. Another current concept holds that an increased amount of this lipogenically active but glycolytically impaired insulin is the mechanism producing obesity in diabetes as a premellitic sign. Despite changed concepts the importance and effectiveness of prophylactic weight control in the premellitic stage, and as the fundamental treatment in all stages of obesity-diabetes remains the same. The order of preference in the addition of specific drugs to the dietary treatment of obesity-diabetes is anorexigenic agents, phenformin, single sulfonylureas, and combined chlorpropamide-phenformin. Insulin is the therapy of last resort in this usually mild form of diabetes. There is great potential usefulness for oral hypoglycemic combination therapy (with steroids temporarily if necessary) as a replacement for insulin in the treatment of immunologically-produced insulin resistance.