Forty patients with different clinical and electrophysiological types of myoclonus were treated with piracetam (18-24 g per day, p.o.) alone, or with other drugs (clonazepam, sodium valproate, and primidone) in different combinations. Piracetam in monotherapy improved the electrophysiological abnormalities in patients with cortical reflex myoclonus, but had no useful clinical effect. Sixteen patients obtained benefit from piracetam when given in combination with other antimyoclonic drugs; improvement was dramatic in two patients, moderate in seven and mild in seven. All patients showing some response to piracetam had myoclonus of cortical origin; however, five other patients with similar cortical myoclonus failed to improve when piracetam was added. Tolerance was excellent and side effects were minimal and transient. It is concluded that piracetam probably has an antimyoclonic action, but its potential value as a therapeutic tool for disabling myoclonus requires further study.