Among the disputed questions considered in this presentation are (1) Relationships between a) the known metabolic abnormalities in diabetes and the development of microangiopathy, and b) insulin antibodies and nodular glomerulosclerosis; (2) Sensitivity to insulin and availability of insulin in idiopathic diabetes mellitus and in other conditions associated with impaired glucose tolerance; (3) The role of pituitary growth hormone in the etiology of idiopathic diabetes; (4) The status of “bound insulin,” ILA, etc.; and (5) The identification of the “synalbumin” insulin antagonist as the B chain of insulin. Also included are the presentation of data on insulin and growth hormone-secretory responses to glucose loading in obese and nonobese diabetic and nondiabetic subjects and a discussion of the interrelationships among the peptide hormones, glucose and free fatty acids in blood.