Diabetes mellitus results from an absolute or relative deficiency in insulin secretion and a resistance of target tissues to the action of insulin, in proportions that vary with the type of the disease. The shortage of insulin can be corrected by administration of exogenous insulin or stimulation of pancreatic beta-cells with sulphonylureas. However, insulin resistance remains a major therapeutic problem. Here, Sonia Brichard and Jean-Claude Henquin review the recent discoveries that indicate a possible role for vanadium in management of the disease. In vitro, vanadium salts mimic most effects of insulin on the main target tissues of the hormone, and in vivo they induce a sustained fall in blood glucose levels in insulin-deficient diabetic rats, and improve glucose homeostasis in obese, insulin-resistant diabetic rodents. Recent short-term clinical trials with vanadium salts also seem promising in type II (non-insulin-dependent) diabetic patients in whom liver and peripheral insulin resistance was attenuated, indicating the therapeutic potential of vanadium salts, pending demonstration of their long-term innocuity.