In the experimental rat model of diabetes a slowing of nerve conduction velocity and a resistance to ischemic conduction failure have been found as an indication of polyneuropathy. The same electrophysiological abnormalities have been demonstrated in a model in which healthy rats are kept under hypoxic conditions (10% O2) for a 10-week period. Two factors are held responsible for the development of diabetic polyneuropathy: metabolic deterioration and hypoxia. However, until now the relative roles of metabolic deterioration and hypoxia in the development of polyneuropathy have not been settled. To test both explanations further with more sophisticated electrophysiological techniques, the H-reflex (motor and sensory NVC) and the stimulated SF-EMG (measures terminal nerve branch and neuromuscular transmission) were measured in 3 groups of 10 rats, a healthy control group, a diabetic group, and a hypoxic group, every 5 weeks, for 6 months. In the control rats an age-related increase in motor and sensory conduction velocity was found, whereas in the diabetic rats as well as in the hypoxic rats a marked decrease in sensory and a slight decrease in motor nerve conduction velocity was observed. The jitter measured in the stimulated SF-EMG was significantly increased in both the diabetic and the hypoxic group. The results of the present study support the possible role of hypoxia, in addition to metabolic factors, in the development of experimental diabetic neuropathy.