BACKGROUND Toxoplasmosis is a parasitic disease which may cause some laboratory symptoms in infected individuals. One of the main ways to transmit this organism is placenta to the fetus pathway. If this transmission occurs in the 3(rd) month of pregnancy, the abortion, central nerve system and ocular disorder will happen. Because of this issue, the precise technique for the detection of Toxoplasma antibodies such as immunoglobulin G (IgG) and immunoglobulin M IgM are important, as they contain ELISA and ELISA avidity. METHODS In this survey, the main samples are serum and amniotic fluid that were collected from 48 pregnant women infected with Toxoplasma gondii in Shariaty hospital. This survey is attempted to design ELISA avidity kit in Tarbiat Modates University. RESULTS The results from this survey show that, in these total pregnant women the infection by T. gondii has occurred and many of them are infected currently. CONCLUSIONS In the simple ELISA technique, the only antibody that can be detected precisely is IgM; however, using this technique the IgG antibody can also be detected. In this new technique or ELISA avidity, in addition to detection of IgG antibody against T. gondii, the month of transmission of Toxoplasma is also interpreted.