A size selected genomic DNA library was constructed using DNA extracted from Taenia saginata. The DNA was digested using the restriction enzyme EcoR1 under star conditions and the 2-4 kbase fraction, selected following sucrose density-gradient separation, was cloned in the bacteriophage lambda gt 10. A panel of cestode DNAs including Taenia saginata, Taenia solium, Taenia taeniaeformis, Taenia crassiceps, Echinococcus granulosus and DNAs of bovine, porcine and human origin were used in conjunction with hybridization analysis to identify two recombinant bacteriophages. The first probe, designated HDP1, reacted specifically with T. saginata DNA. The second, designated HDP2, reacted with DNA from both T. saginata and T. solium but not the other DNA samples and thus provided a general reagent for positive identification of fragments of Taenia spp. proglottides of human faecal origin. If used in conjunction the two DNA probes allow positive identification of T. saginata. In the clinical situation it is important to be able to distinguish T. saginata and T. solium infections and DNA probes such as these may be useful in such differentiation.