66 placentas of mothers with protodiabetes or of the White-classes A/a, respectively, are investigated morphologically. The results are correlated with the clinical findings. Complications during pregnancy as well as the perinatal mortality (5.7 per cent) are less frequent in early stages before the diabetes become manifest. Severe diabetic disturbances of placental maturation we have found in protodiabetics in 15.4 per cent, in the White-classes A/a in 18.9%. In the White-classe D the frequency is 49.5 per cent. Accordingly, the diagnostic possibilities are smaller than in cases with manifest diabetes mellitus. Diabetic disturbances of placental maturation can be demonstrated already in few cases of the material in protodiabetics and in patients with glucosuria during pregnancy and with suspicion of diabetes mellitus, but without diabetic fetopathy. Therefore in our opinion diagnosis of diabetic metabolic disorder may be possible by some morphologic criterias of the placenta in very early stages of diabetes before clinical manifestation.