Several structural and functional similarities between nerve growth factor and insulin have been described. Diabetes mellitus, a disease with absolute or relative deficiency of insulin is frequently associated with peripheral neuropathy whose physiopathological mechanisms are obscure. In this study, we measured serum levels of NGF in 18 patients with diabetic neuropathy and 9 healthy controls; patients with diabetic neuropathy had lower levels of NGF than controls (p less than 0.01). When patients were separated in two groups according to degree of impairment of motor nerve conduction velocity, those with more than 10% of impairment, had lower levels of NGF than those with less than 10% of impairment, or controls. It was found a correlation between NGF levels and decrease of motor nerve conduction velocity; then, diabetic neuropathy seems to be associated to low serum levels of NGF, pointing out a possible role of NGF in the pathology of diabetic neuropathy.