DNA isolated from a newly described taeniid from Taiwan which shows adult characters indistinguishable from those of Taenia saginata was compared to DNA from T. saginata and nine other cestodes by restriction endonuclease digestion of genomic DNA and Southern blot analysis using 32P-labeled total cestode RNA and cloned ribosomal RNA gene fragments as probes. Hybridization patterns of Taiwan Taenia DNA revealed distinct variations from that of T. saginata and Taenia solium as well as all other cestode DNAs examined; however, similarities in restriction maps and sequence data between cloned ribosomal gene fragments from Taiwan Taenia (pTTr 3.1) and T. saginata (pTSgr 3.1 and PTSgr 2.4, respectively) suggest close evolutionary relatedness between these two taeniids. DNA sequence amplification from genomic DNA using oligonucleotide primers homologous to regions on both the 2.4- and 3.1-kb fragments was able to delineate between Taiwan Taenia and T. saginata by generating 1.0- and 0.29-kb fragments, respectively. Results demonstrated that Taiwan Taenia is not exclusive to Taiwan but exists in other parts of Eastern Asia and that adult morphology is insufficient for its detection in other locations. Results further support biological data indicating that Taiwan Taenia and T. saginata, although similar morphologically, are distinct genotypes.