The number of Neurons and the Neuronal and glial density per volume of the facial and the vestibural nuclei in two brain stems on each side in man, monkey and dog were counted. The average number of Neurons in the facial nucleus in man (12,500) is greater than in the monkey (4,600), but lower than in the dog (15,800). On the contrary, in the vestibural nuclei the total number of Neurons in man (245,00) is greater than in the monkey (143,000) as in the dog (134,000). The Neuronal density varies considerably in different nucei and different species of animals. At the same time, the glial density is much more even. In all the nuclei the glial density is highest in the dog, lower in the monkey and still lower in man.