The authors report changes in the bioelectric activity of the brain in acute, severe, suicidal poisoning with hydrazide. The observed group comprised 10 patients, 9 were admitted in coma, 7 had convulsions. Normal EEG tracing was found in a case of combined poisoning with hydrazide and diazepam. Low-voltage tracings with a tendency for bioelectric inactivity development were observed in 2 cases with lethal outcome. In the remaining cases high-grade diffuse changes were present, in three of them seizure activity was present additionally. Full evolution of bioelectric changes was observed in 5 patients. The time of return of normal activity ranged from several days to several weeks. Very slow improvement with incomplete normalization was found in mixed intoxication (hydrazide, barbiturates) treated with haemodialysis. The authors think that in cases with persistence of EEG changes despite regression of acute signs of poisoning intensive treatment with vitamins B should be continued.