Severe weakness of lower cranial and girdle muscles has been found in 4 subjects among 20 dialysis patients treated with carnitine in order to correct their high plasma triglyceride level. Neurophysiological investigation showed an impairment of neuromuscular transmission with short-term reduction of evoked muscle responses to repetitive stimulation and the presence of "post-activation exhaustion phenomenon" 3 min after the train. Both the weakness and the neurophysiological findings were less pronounced after edrophonium. These findings suggest a hemicholinium activity of carnitine at synaptic level.