The phylum Echinodermata is well known for its extensive regenerative capabilities. Although there are substantial data now available that describe the histological and cellular bases of this phenomenon, little is known about the regulatory molecules involved. Here, we use an immunochemical approach to explore the potential role played by putative members of the transforming growth factor-beta (TGF-beta) family of secreted proteins in the arm regeneration process of the crinoid Antedon mediterranea. We show that a TGF-beta-like molecule is present in normal and regenerating arms both in a propeptide form and in a mature form. During regeneration, the expression of the mature form is increased and appears to be accompanied by the appearance of an additional isoform. Immunocytochemistry indicates that TGF-beta-like molecules are normally present in the nervous tissue and are specifically localized in both neural elements and non-neural migratory cells, mainly at the level of the brachial nerve. This pattern increases during regeneration, when the blastemal cells show a particularly striking expression of this molecule. Our data indicate that a TGF-beta-like molecule (or molecules) is normally present in the adult nervous tissues of A. mediterranea and is upregulated significantly during regeneration. We suggest that it can play an important part in the regenerative process.