Reflex excitability of spinal centers of hand muscles was examined in normal subjects and patients with traumatic lesion of forearm nerves. Central and peripheral muscle responses were evoked by stimulation of homonymous and heteronymous nerves. Patients with median and/or ulnar nerve lesion showed the heteronymous abductor pollicis brevis and abductor digit minimi H-responses. The cause of appearance of heteronymous responses is supposed to be actualization of latent heteronymous monosynaptic connections following traumatic lesion and afferent deprivation. It seems obvious that activation of heteronymous pathways corresponds to the process in afferent system known as "revitalization" of median-to-ulnar anastomoses after damage.