Both the males and females of Speleomantes flavus, S. genei, S. imperialis and S. supramontis possess gland clusters in the dorsal skin of the tail base, consisting of large, closely contiguous, serous or mixed units. Structural and ultrastructural investigations revealed consistent homogeneous features in the glands from the four species and obvious homologies between these and the serous and mixed cutaneous glands of the back skin. Seasonal changes were not observed in the secretory activity of the tail base glands. It is suggested on the basis of these findings that tail base glands play a role possibly involving defensive strategies or, alternatively, the production of pheromone-like substances which may help the animals to recognize each other. The occurrence of tail base glands in both plethodontid subfamilies and respective tribes, found in the present study and bibliographical data, is regarded as a symplesiomorphy. Further suggestions on the phylo. genetic significance of this anatomical character may, however, be derived from its distinctive occurrence and functional role in the various plethodontid groups. Present findings suggest that tail base glands represent a plesiomorphous character in the Speleomantes species observed, whereas the condition of these gland clusters, described in some New World Plethodontidae, is assumed as a synaphomorphy.