Four cases of mild botulinus type B intoxication are reported with the clinical neurophysiological studies. Electromyographically tetanic stimulation of the N. ulnaris initially led to tetanic potentiation of the muscle action potential. After an interval without any symptoms tetanic reduction became apparent between the fourth and seventh week of the illness. The electroneurographic finding was normal during the observation period of three months. Infrared reflex pupillographic studies revealed that the cholinergic autonomous synapses were disturbed for a period much longer than the symptoms clinically established. The speed at which the pupillographic findings returned to normal varied considerably according to the patient. Electroencephalographic results indicated generalized groups of slow high amplitude waves in three of the four cases during the period of observation. The pathophysiology of botulinus intoxication is discussed with a consideration of the literature and the results of this study.