In five monkeys, studied after a number of metrazol-induced convulsions it was observed that:1. Histopathological changes in the central nervous system are not always present. When they occur they are not proportional to the number of convulsions, to the dosage of the drug or to the duration of the seizures.2. The alterations, if found, are very mild, considerably milder than the ones described after insulin treatment. They consist of small groups of cells which present acute degenerative changes or at times the severe type of degeneration described by Nissl.3. In two cases examined with the Pick-worth method anemia of external cortical layers, anemic and hyperemic foci in the inner areas or generalized breaking up of the capillary blood columns network were observed.4. These vascular modifications appear to be of functional character and do not seem to be responsible for the cellular lesions inasmuch as they are not generally accompanied by nerve cell changes.5. Interstitial and parenchymatous nephritis was always found and the question of its possible relationship to some pre-existing pathological conditions aggravated by the metrazol, is raised.6. A pigment, which gives no Prussian blue or Gmelin reaction was noted in the liver in 4 of the 5 cases examined.Abstract Teaser