Quantitative measurements of skin capillary resistance were carried out in twelve control subjects, eight long-term diabetics with proliferative retinopathy, and in sixteen diabetics hypophysectomized for diabetic retinopathy. Ten individual measurements of capillary resistance were performed on each subject. All subjects but two were less than fifty years of age. In the control subjects, the mean capillary resistance ranged from 144 to 222 mm. Hg. With the exception of two, all had mean values between 150 and 200 mm. Hg. The long-term, nonoperated patients demonstrated fragile capillaries. All but one of these patients had mean values below 150 mm. Hg (range 90 to 160 mm. Hg). Most of the hypophysectomized diabetics had a mean capillary resistance above 200 mm. Hg (range 162 to 372 mm. Hg). The values were significantly increased in comparison with the results obtained in the control subjects and in the nonoperated diabetics.