1. Insulin-like effects of vanadium compounds have been reported in various experimental conditions. Effects of vanadate on the decreased beta-adrenergic responsiveness of the rat duodenum due to streptozotocin diabetes were investigated to determine its influence on diabetic gastro-intestinal complications as well as its effects on the carbohydrate metabolism. 2. Administration of sodium orthovanadate to streptozoticin-diabetic rats in drinking water (0.7 mg/ml) for 4 weeks resulted in an improvement of carbohydrate metabolism noticed by increased serum levels of insulin and decreased blood levels of glucose as reported in previous studies. 3. Vanadate treatment of streptozotocin-diabetic rats also corrected the diabetic changes in the beta-adrenergic responsiveness of the rat duodenum to salbutamol suggesting a beneficial effect on the diabetic complications of rat gastro-intestinal tract. The same treatment with vanadate did not cause any alteration in the beta-adrenergic responsiveness of isolated duodenum from non-diabetic rats. 4. From the findings obtained, it is concluded that vanadate possesses an insulin-like effect on the beta-adrenergic responsiveness of the rat gastro-intestinal tract. Since vanadate treatment did not alter the beta-adrenergic responses of isolated duodenum from non-diabetic rats it seems likely that the insulin-like effect of vanadate is dependent on increased responsiveness of the gastrointestinal tract to circulating insulin.