To the Editor— Rix's letter (217:480, 1971) recommending primary nerve repair in combined nerve and tendon lacerations, and the subsequent letters of Raskind et al (217:1864, 1971) and Cramer (219:1213, 1972) presented interesting discussions of the management of peripheral nerve injuries. We are in the process of reviewing data from a serial study 1 of 376 peripheral nerve injuries in 223 patients, and I would like to offer some preliminary observations and theoretical support for Rix's conclusions. Our study was prospective, and included a protocol in which clinical and electromyographic examinations were serially performed. In studying regeneration of motor nerves we found that even in the most successful cases when full clinical strength returned, innervation as determined electromyographically by counting motor units was less than complete. Apparently, following peripheral nerve injury, greater-than-normal numbers of muscle fibers become incorporated in each motor unit, and muscle fibers undergo hypertrophy. Similar studies of