High molecular weight DNA samples free of contaminating proteins and RNA obtained from one isolate (of Guangzhou origin) of Cysticercus tenuicollis and five isolates (of Tianjin, Harbin, Lanzhou, Shenyang and Zhengzhou origin) of Cysticercus cellulosae were subjected to thermal denaturation, restriction endonuclease digestion, Southern blotting and hybridization analysis. C. cellulosae DNA showed a melting temperature (Tm) of 82 degrees C corresponding to a 31% GC content whereas C. tenuicollis DNA melted at 85 degrees C suggesting 38.3% GC content. Visual inspection of ethidium bromide-stained gel showed differences not only between the DNAs of the two species of Taeniid cestodes, but also among the five isolates of C. cellulosae. Furthermore, we used two fragments (1.9kb and 5.5kb) of HindIII-derived restriction fragments of C. cellulosae DNA (Harbin origin) and pTS10 as probes to hybridize the DNAs of the Taeniid cestodes from six origins to detect inter- and intra-species genetic variation, the restriction fragment length polymorphisms (RFLPs) were identified.