RNA secondary structure is essential for RNA function in pre-mRNA splicing, mRNA translation, ribosome assembly and RNA stability. The involvement of DEAD/H RNA helicases in the regulation of these processes has been demonstrated in some cases. To investigate the repertoire of DEAD box proteins expressed in Dictyostelium discoideum, we used PCR techniques to clone two cDNAs coding for DEAD box proteins with high similarity to known yeast proteins: Dictyostelium Hel2A is about 45% identical to Saccharomyces cerevisiae DBP2 and S. pombe dbp2, the yeast homologues of human p68. Dictyostelium Hel2B is about 43% identical to the S. cerevisiae splicing factor PRP28, but has a different domain at the N-terminus, which is unique for Dictyostelium discoideum. Using a polyclonal antibody directed against a DEAD box peptide we show differential expression of three DEAD box proteins during the developmental cycle of Dictyostelium.