The quantitative stereological method is applied to a study of the number of neurons in three different areas in the brains of an animal model, the Mongolian gerbil. The simplicity and accuracy of the method is emphasized. The usefulness of the method and the model is mentioned especially focusing on the major disabling disease in the Western world today, cerebrovascular disorders. Some results are presented to give an idea of the maximum number of neurons in these animals within the delineation of the brain areas here applied.