Resistance to ischaemia of small afferent nerve fibres in diabetes mellitus. Thermal thresholds were measured in the left forearms of 26 healthy subjects and 10 patients with diabetes mellitus during ischaemic compression block. During the period when ischaemic block of large fibres caused paraesthesia and loss of touch sensation, the cold threshold rose in normals. The cold threshold was less clearly elevated and the warm perception remained unaltered by ischaemia in diabetics. These results show that not only large afferent and efferent nerve fibres but also thinly myelinated A delta and unmyelinated C fibres are resistant to ischaemia in the diabetic nerve. 