Abstract: We have constracted a genomic DNA library of Toxoplasma gondii (ZS2 strain) and screened out a specific DNA sequence for T. gondii. The restriction map of the cloned DNA fragment (1.1kb) was analysed. The Southern and dot-blot analyses showed that the 32P-labeled cloned DNA fragment hybridized to the parasite DNA, DNAs from peripheral white blood cells and thymus of baby pigs artificially infected with T. gondii and DNAs of T. gondii- positive anencephalus and hydrocephalus, but did not hybridize to DNAs from controls, i. e., normal human and baby pig peripheral white blood cells, spleen of normal mouse, Plasmodium falciparum, Pneumocystis carinii and pBR322. As few as 100 T. gondii parasites or 500pg purified DNA from T. gondii can be detected by dot blot hybridization. This established DNA probe method was specific and sensitive and has been successfully used in detecting various cases infected with T. gondii.