A total of 540 women, in two clinical groups, differing by information obtained during the interview, were investigated. Several observations were made. It was found that values of titers in indirect immunofluorescnece test (OIF) in consecutive trimesters of pregnancy in the same women are not changing in 50%, in about 10% differ by some to 10 times, and in remaining patients move by one grade of serum dilution with a tendency to increase. This seroconversion regards about 17% and from negative to positive in 10%. High convergence of results obtained by OIF and ELISA tests for IgG antibodies was detected. The level of specific antibodies determined by ELISA test can be analyzed basing on parameters of distribution of quantitative feature and coefficients of linear correlation. Secondary specific antibodies against Toxoplasma of the IgM class may appear in every trimester of pregnancy with positive antibodies of IgG class which in some cases remain unchanged for several months regardless of treatment with anti-toxoplasmal drugs.