Morphological and neuroelectrical changes of the skeletal muscle fibres after various types of injury to the nerve was studied in monkey. The percentage of normal and atrophic muscle fibres after various types of injury to the nerve was compared with the proportion of innervated and denervated muscle as shown by the position of the bend (kink) on the I.D. at corresponding stages. It was found that the pattern and the position ofthe I.D. curve when considered together only gave an approximate estimation of the proportion of all innervated and denervated muscle fibres as well as the condition ofthe muscle after denervation.