The purpose of this study was to determine the effect of testing for IgG avidity in the diagnosis of Toxoplasma gondii infection in pregnant women. IgG avidity test was investigated with microELISA in 68 pregnant women whose serologic tests were found positive for toxoplasmosis. The patients had been sent to the Microbiology Laboratory, Izmir Atatürk State Hospital, from the Obstetrics and Gynecology Outpatient Clinic, in the period between January 2007 and May 2008. Low avidity was found in 83.3 % of the patients who were Toxoplasma IgM positive, and high avidity in 59.7 % who were Toxoplasma IgM negative. Of patients with high avidity IgM was positive in 1 (2.6%) and negative in 37 (97.4%). It was concluded that to differetiate acute toxoplasmosis from past infection, avidity test should be carried out together with Toxoplasma IgG. IgM and IgA tests.