This study was designed to evaluate the gene expression level of IFN-γ in murine leukocytes treated by Toxoplasma gondii products in vivo using quantitative real time-PCR (Q-PCR) method. The mice considered as test groups were treated separately by Toxoplasma lysate product (TLP), excretory/secretory products (ESPs) obtained from cell free and cell culture media as well as active tachyzoites. The mice in the control group received phosphate buffered saline (PBS). The peritoneal leukocytes of the mice were harvested separately and their total RNA was extracted, converted to cDNA, and the gene expression level of IFN-γ was measured in all of the test groups relative to the control one. The results showed that the gene expression level of IFN-γ was decreased in the groups of the ESP from cell free medium (P=0.03), the TLP (P=0.02), and the active tachyzoite (P=0.16). Moreover, there was no significant difference statistically for the group of the ESP from cell culture medium (P=0.33). The findings revealed for the first time that the TLP and the ESP from cell free medium contain molecules that are capable of downregulating the expression of IFN-γ. Therefore, the question arises as to which molecules in these two products are involved in this process?