The immune response to Trypanosoma cruzi was studied in our hospital in 937 pregnant women(PW) and their 929 newborns(NB), group I; 4 NB from this center not included in the first group, group II and 35 NB derived from other centers, group III. Two positive results among indirect hemagglutination (IHA), complement fixation(CF) and indirect hemagglutination(IHA), complement fixation(CF) and indirect immunofluorescence(IIF) tests were considered as the criterion of previous infection with T. cruzi in PW. The presence of T. cruzi in blood, explored in fresh smears by serial micro-hematocrite and/or by xenodiagnosis, was the only criterion to define infection in NB. All NB were followed up by direct agglutination (DA) with or without 2 mercaptoethanol (DA-w2ME, DA-wo2ME) and IIF in order to establish the specific antibody kinetics. Clinical studies on NB with T. cruzi infection include routine laboratory tests. Benznidazole (3 to 7 mg/kg/day) and, in 1 case, nifurtimox (15 mg/kg/day) were employed as therapeutic agents. T. cruzi infection was confirmed in 149 PW(15.9%), table I. These chagasic mothers delivered 6 chagasic NB (CCHD-NB), (4%). Diagnosis of congenital Chagas' disease accounted for a total of 12 NB out of the 968 studied. 4 out of them were positive by both microhematocrite and blood smears and 7 by microhematocrite alone. Xenodiagnosis was performed in 2 NB resulting positive in both cases, table II. The most usual clinical findings included hepatomegaly (present in all cases), splenomegaly 8/12, jaundice 10/12 and prematurity 5/12, table 3. Laboratory findings showed anemia to be of hypochromic microcytic type in all cases.(ABSTRACT TRUNCATED AT 250 WORDS)