1. The results of electrodiagnostic tests reveal the level and progress of nerve lesions. 2. The findings in a myopathic lesion are: a) a normal SD curve; b) no fibrillation on the E.M.G.; c) on volition a full interference pattern-because motor units have not been lost, but only muscle fibres within the units; d) the action potentials are short in duration, polyphasic and of low amplitude; e) conduction times are normal. 3. In peripheral nerve affections these findings are evidence of denervation: a) a sluggish response to a long duration current; b) a kinked SD curve; c) fibrillation at rest on the E.M.G.; d) a reduced interference pattern of motor unit action potentials on volition; e) a preponderance of polyphasic action potentials of long and short duration; f) slowing of conduction times. 4. Evidence of reinnervation is given by: a) a kink in the SD curve; b) the appearance of a response in the muscle to nerve stimulation; c) a progressive increase in conduction velocity; d) the appearance of polyphasic action potentials on volition; e) fibrillation becoming more difficult to detect. 5. The following findings suggest a lesion of the anterior horn cell: a) difficulty in detecting fibrillation, and a relatively normal SD curve in the presence of marked wasting. (Intact axons have "mopped up" denervated fibres.) b) Marked reduction in interference pattern with ‘giant units’. c) Normal conduction velocity