IN CLINICAL practice, "myoclonus" is often used to describe any sudden involuntary movement or jerking that can not be otherwise classified. These movements occur in a wide variety of diseases and in varied forms so that the word myoclonus needs to be qualified whenever it is used. Certain kinds of rhythmic myoclonus eg, palatal myoclonus (myorhythmia), experimental Newcastle disease encephalomyelitis, and epilepsia partialis continua are easily distinguished from the more protean, irregular, jerky, types of myoclonus. The latter tend to be asynchronous, variable in force and complexity, and may involve any muscle, combination of muscles, or the entire body. Halliday1 has provided an extensive review of the clinical incidence of myoclonus. Kinsbourne,2 in 1962, described a generalized myoclonic disorder of late infancy with acute onset and long duration. This condition had not been clearly delineated prior to his report, although several similar cases were reported as ocular