Octreotide, a synthetic analogue of somatostatin, may improve metabolic control and reduce GH and glucagon levels in insulin-dependent diabetic patients. We report hereto the case of an insulin-dependent diabetic patient in whom the subcutaneous continuous infusion of octreotide (150 micrograms/daily for six days) resulted ineffective on blood glucose levels, GH and glucagon. However, when octreotide was administered mixed together with aprotinin-an inhibitory of proteolytic enzymes (10,000 I.U. daily), it had lowering effect on blood glucose levels, GH and glucagon. We suggest the possibility that a local subcutaneous enzymatic degradation of octreotide may have occurred and that this degradation was blocked by aprotinin.