The occurrence of organ-specific, cellular hypersensitivity against pancreatic components was examined in twenty-two diabetics by means of the leucocyte migration test. An extract was prepared from pooled porcine pancreatic glands, in which atrophy of the exocrine tissue had been induced by ligation of the pancreatic duct. A specifically altered in vitro reactivity to the pancreatic preparation, consistent with a state of organ-specific, cellular hypersensitivity, was demonstrated in the diabetic group as compared to a control group. Intracutaneous injection of the same preparation in six diabetics with a positive in vitro reaction induced a typical delayed type reaction in four.