The aim of the study was to isolate genes coding for stage-specific antigens of T. spiralis. Such antigens may then be associated with local and systemic immune responses against adult T. spiralis. Recombinant clones were obtained with an adult stage specific probe from a cDNA library of three-day old adult T. spiralis. Several cDNA clones encoding the same peptide were identified and their stage specificity was confirmed by northern blot analysis. Three independent clones were fully sequenced, and the resulting sequence found to code for a 487 amino acid peptide with a deduced molecular weight of approximately 55 kDa. Sequence analysis showed that the 55 kDa peptide contained putative DNA binding motifs, suggesting that this protein may be involved in transcriptional regulation during the early development of the parasite.