DNA and RNA in combination have been prepared and characterised from the hydatid disease organisms, Echinococcus granulosus and Echinococcus multilocularis. The DNA obtained is of high molecular weight, pure and can be cleaved by restriction enzymes, thereby facilitating future production of genomic DNA probes for studies of Echinococcus gene expression. Moreover, cloned DNA segments from Schistosoma mansoni hybridise strongly to Echinococcus DNA following restriction and Southern blot analysis. The extracted RNA is functional and has been translated in vitro. The major translated polypeptides and antigens have been identified, and the technique can now be used to analyse differential gene expression during development and differentiation of the hydatid organisms and to identify specific polypeptide antigens which may have potential as immunodiagnostic reagents.