PCR was compared with capture ELISA and immunoblotting for the detection of Toxoplasma gondii in sera of acutely infected mice. One hundred animals were inoculated intraperitoneally with 5000 trophozoites of RH strain and five of them were killed every 3 h from 3 h to 21 h post infection (p.i.), and every day from day 1 to day 7 p.i.. No assay detected the parasite from 3 h p.i. to 15 h p.i. PCR was the most sensitive assay and detected the T. gondii from 18 h p.i., whereas the other assays detected it only from day 1.