1. Acute effects of Karwinskia humboldtiana (Kh) ingestion were studied in some cerebral motor regions. 2. In motor cortex, widening of Virchow-Robin spaces and hyperchromasia occurred throughout the study. 3. In CA1 region of hippocampus, hyperchromasia, swelling of cell nuclei and neuronal shrinkage; were observed at the various stages. 4. In caudate nucleus, cell shrinkage and nuclear swelling occurred throughout the study. 5. Cell death images were observed in all areas studied. 6. It is suggested that a toxic effect is produced by Kh fruit, and that tissue damages may be closely related to the motor non-paralytic disturbances observed after its ingestion.