Concentric needle electrode electromyography was carried out and motor nerve conduction measured in 35 infants suffering from myelomeningocele at a mean age of 5.1 hours. Electromyographic signs of denervation were inconspicuous and the findings suggested that a lesion of the upper motor neurone — with or without spinal shock — was more important than one of the lower motor neurone. There was a highly significant reduction in motor conduction velocity of lower limb nerves. It is postulated that this is due to retarded myelination of lower limb nerves.