The ammonia and glutamine content in the brain of rats is not increased by the action of caffeine and low doses of sodium bromide. Conversely, the animals' behavior and the content of ammonia and glutamine in the brain rises under the effect of large doses of sodium bromide. Increase of the ammonia and glutamine content in the brain occurring in carbon tetrachloride poisoning does not drop noticeably under the effect of caffeine or sodium bromide. Investigations of rats' brain at different intervals after CCl4 administration (in 1–2 hours and in 24 hours) show that the increase of the ammonia and glutamine content in the brain occurs only when marked injury of the liver tissue takes place, i.e., in 24 hours, not-withstanding the fact that the general condition of rats is particularly grave in 1–2 hours. This confirms the supposition that disturbances of the central nervous system occuring in diseases of the liver may be also due to the action of ammonia.