Three new cases of methyl bromide poisoning (leakage from a fire extinguisher) are reported. Two of these were characterized, after an initial period of coma and myoclonic status, by an action myoclonus. Electrical data are presented. A follow up of 4 and 8 years allowed to study the effect of drugs, two of which (clonazepam and baclofene) being pecularly contributive. The third patient outlived for 5 years in a stuporous state with myoclonus. The anatomical findings consisted mainly of a necrosis of both inferior colliculi with gliosis in the upper brain stem reticular formation and moderate changes in the dentate and pontine nuclei. Their significance is discussed in view of physiological and experimental knowledge.