Necrotic ulcers of the feet are a dangerous complication of the diabetic foot syndrome. Besides peripheral vascular disease (PVD) peripheral neuropathy is an important factor in the pathogenesis of necroses. We examined whether the reserve of circulation during reactive hyperemia at the feet of patients with type I diabetes mellitus with abnormal blood flow (n =17) is decreased compared with diabetic (n =14) and nondiabetic (n = 20) controls. Further we analyzed whether there is a correlation with the oxygen supply of the foot. PVD was excluded by clinical check-up, oscillography, and Doppler ultrasound. The reserve of circulation of the foot was measured during reactive hyperemia and oxygen supply of the foot by oximetry. Abnormal blood flow of the foot was diagnosed by the pulsation index. On examination it was found that the reserve of circulation of diabetic feet with abnormal blood flow is about 52% less than in diabetic and about 50% less than in nondiabetic controls (P<0.005). The decreased reserve of circulation correlates with the oxygen supply of the feet; this is about 21% less compared to diabetic feet with normal blood flow and about 16% less in comparison to nondiabetic feet. The present study shows that diabetic feet suffer from disturbed circulation although there is no evidence of PVD. This disturbed circulation is correlated with a decreased oxygen supply of the feet. Hypoxia during strain could be of great importance in the pathogenesis and treatment of necrotic ulcers of diabetic feet.