Summary.The digestive tract has been examined by light microscopy in 17 subjects with diabetes of early onset, long duration and with various causes of death, in 6 "normal" controls and 10 controls with uremia and/ or hypertension. In the diabetics grave lesions were demonstrated to a large extent in the capillaries and venules of the oral mucosa, and in small arteries and arterioles in the gastrointestinal tract (from the oesophagus to rectum). The capillary and venular lesions were similar to those earlier described in the skin of diabetics. The arterial lesion was characterized by a hyalin, strongly PASpositive, picrinophilic (eosinophilie), richly fat-containing (sudanophilic) wall thickening accompanied by heavy reduction of the lumen, endothelial atrophy and medial degeneration. Similar arterial lesions were demonstrated in the kidneys, pancreas, liver, spleen, adrenal glands, testes, prostate and ovaries. The study suggests that hypertension was not of essential importance to the development of the arterial lesions. It is assumed that the grave arterial lesion accentuates terminally in the course of diabetes, where final complications such as ischemia and adrenocortical overactivity are of pathogenetic significance.