We evaluated 40 diabetic patients (with a duration of the disease longer than 10 years) with diabetic neuropathy, to assess the effect of a good metabolic control maintained for six months on the nervous conduction velocity. The motor nervous conduction velocity (NCV) and the sensory latency and potentials were evaluated in the median and external popliteal nerves. In the groups of patients with a good metabolic control (mean basal glucose blood levels 109 +/- 12 mg/dl, or 6.04 +/- 0.66 mmol/l) there was a significant clinical improvement with improved test results; the NCV if the external popliteal nerve changed from 40.5 +/- 5.9 m/sec to 43.5 +/- 5.8 m/sec (p less than 0.05). An improvement of motor involvement and sensory potentials were found in 35 and 20%, respectively, of group I patients. The differences with those patients without a good metabolic control, in whom no study parameter improved, were significant. These studies apparently show a good metabolic control may reverse or at least improve diabetic neuropathy. However, wider studies are required to elucidate whether diabetic neuropathy is reversible or not.