Microvascular factors have been implicated in the pathogenesis of human diabetic neuropathy. The extent of microangiopathy was assessed in 15 diabetic patients with clinically mild neuropathy and compared with eight age matched control subjects. Endoneurial capillary density was reduced (p less than 0.04) and correlated significantly with reduced myelinated fibre density (p less than 0.01). Both basement membrane area (p less than 0.0001) and endothelial cell profile number per capillary (p less than 0.002) were significantly increased in diabetic patients and correlated significantly with both neurophysiological and neuropathological measures of neuropathic severity. There was no evidence of endothelial cell hypertrophy as assessed by either cross sectional endothelial cell area or a reduction in luminal size. Furthermore, the percentage of closed vessels did not differ between diabetic patients and control subjects and failed to relate to measures of neuropathic severity. It was concluded that microvascular abnormalities are prominent in patients with clinically mild human diabetic neuropathy, and that these data provide further support for the role of endoneurial capillary disease in the development of this condition.