A novel 100-150-residue domain has been identified in the human splicing factor YT521-B and its Drosophila and yeast homologues. Homology searches show that the domain is typical for the eukaryotes and is particularly abundant in plants. It is predicted to adopt a mixed alpha-helix-beta-sheet fold and to bind to RNA. We propose the name YTH (for YT521-B homology) for the domain.