Abstract Objective To investigate acute changes in nerve conduction associated with glycemic control. In diabetes, nerve dysfunction can result from reversible metabolic factors associated with hyperglycemia, as well as structural changes. Methods Multiple nerve conduction parameters including F-wave latencies were measured in 47 diabetic patients with prominent hyperglycemia before and after intensive insulin treatment. Results Four weeks after the start of treatment, there was a significant improvement in minimal F-wave latencies of the median ( P<0.001) and tibial ( P<0.001) nerves, and in distal latencies ( P=0.01) and sensory nerve conduction velocities ( P<0.001) of the median nerves. Amplitudes of motor and sensory responses did not change significantly. These findings were similar for patients with type 1 ( n=8) and those with type 2 ( n=39) diabetes. Patients with poorer glycemic control or milder neuropathy tended to show greater changes after treatment. Conclusions Glycemic control quickly alters the speed of nerve conduction. F-wave latencies and conduction times across the carpal tunnel are very sensitive parameters. Significance Serial nerve conduction studies can detect reversible slowing of nerve conduction presumably caused by metabolic factors, such as decreased Na +/K +-ATPase activity, the altered polyol pathway, and tissue acidosis.