A case of high levels of specific IgM antibodies registered by the immunosorbent agglutination assay (ISAgA) in a pregnant woman with a history of toxoplasmosis is reported. The patient had acute lymphoglandular toxoplasmosis diagnosed serologically by increases in the specific antibody titer detected by the Sabin-Feldman test (SFT) and pathohistologically 12 years before pregnancy. In pregnancy, she had stable titers of specific antibodies registered by the SFT, enzyme-linked immunosorbent assay (ELISA), indirect fluorescent antibody test (IFAT), indirect hemagglutination test (IHAT) and direct agglutination test. Specific IgM antibodies were detected by the ISAgA but not by the IgM-IFAT, IgM-ELISA and IgM-IHAT. She had a normal pregnancy and gave birth to a clinically healthy baby who had a negative ISAgA finding at 7 days of age. This case indicates that ISAgA is not necessarily a marker of recent infection and is therefore not reliable for the diagnosis of toxoplasmosis in pregnancy.