The mechanisms which underlie the development of Charcot joints and foot ulceration are poorly understood. The present study using non-invasive Doppler techniques demonstrates that in the neuropathic leg, the arteries are rigid, peripheral blood flow is increased and associated with arteriovenous shunting. We studied 10 diabetics with severe neuropathy (including five with Charcot changes), 16 diabetics without neuropathy and 10 control subjects. Markedly abnormal blood velocity profiles (sonograms) were demonstrated only in those patients with severe neuropathy. They showed increased diastolic flow (indicated by a reduced Pulsatility Index of 2.88 +/- 0.8 (mean +/- SD) compared with 9.53 +/- 4.0 (p less than 0.001) in the diabetics without neuropathy and 10.8 +/- 3.7 (p less than 0.001) in the control subjects) suggesting arteriovenous shunting. Increased rigidity was indicated by decreased transit times -57 +/- 6.3 ms (mean +/- SD) in the diabetics with neuropathy compared with 66 +/- 7.6 ms (p less than 0.01) in the diabetics without neuropathy and 67 +/- 9.1 ms (p less than 0.05) in the control subjects. This was accompanied by raised ankle systolic pressures -199 +/- 22 mmHg (mean +/- SD) in the diabetics with neuropathy compared with 151 +/- 15 mmHg, (p less than 0.001) in the diabetics without neuropathy and 146 +/- 18 mmHg (p less than 0.001) in the control subjects. Medial wall calcification occurred almost exclusively in the neuropathic subjects. These alterations in blood flow which include arteriovenous shunting may be important in the pathogenesis of complications of the neuropathic leg.