Ten patients affected by various myoclonic syndromes were tested with drugs acting on cerebral serotonin metabolism and with clonazepam (CZP). After L5HTP or serotonergic drugs administration a clear cut improvement was observed in the 2 patients affected by Ramsay-Hunt syndrome, while the patients with myoclonic epilepsy have shown no effect (3 cases) or negative response (1 case). Methysergide was active only in 1 patient affected by progressive erratic myoclonus who had a striking worsening of clinical picture. The main side effects observed were: gastrointestinal distress (L5HTP--4 patients, fenfluoramine--2, quipazine--1, methysergide--2) and cutaneous rash (quipazine--1 case). These results support the possible implication of the serotonergic system in the pathogenesis of myoclonus other than post-anoxic.