Specific IgM anti-Toxoplasma antibodies were sought in 94 serum samples by means of D.S. IgM ELISA. These antibodies were detected in all cases of acute toxoplasmic lymphadenopathy, but up to 13 months from onset of symptoms and in out of 20 patients with chronic toxoplasmosis and in one out of 20 seronegative individuals. They were neither detected in samples from 4 infants with high IgG IFAT titres associated with hydrocephalus and cerebral calcification, nor in samples from patients containing rheumatoid factors and those with lymphoma or infectious mononucleosis. Thus the detection of IgM antibodies seems non decisive mean for identifying infected infants and for determination of the exact date of acquiring the infection.