The amount of afferent fibres to the Telencephalon of Amphibians has been estimated in three species of Anurans (Bufo bufo, Rana esculenta and Xenopus laevis) to verify if the differences in cytoarchitecture of the pallial primordia of Anurans could be due to the different amount of the entering olfactory fibres. The present results show that the primary olfactory afferent to the telencephalon is more prominent in Bufo that in Rana and Xenopus. Our observations have also made it evident that the ultrastructure of the unmielinated olfactory nerves of Anurans is very nearly comparable to that of the fila olfactoria of Mammals. Nevertheless the ultra structure of Anurans' olfactory nerve shows some peculiarities: i) the basement membrane does not entirely enclose the Schwann cell; ii) neurotuboli and neurofilaments are present together in the olfactory fibres; iii) glial-like cells, provided with fibrils, and desmosomes are also interposed between the Schwann cells.