A study was carried out on T. cruzi infection in pregnant women in the Guemes area in Salta province; the rate of infection was 12.3%. Of newborn children studied by the microhematocrit technique, 8.8% were diagnosed with Chagas' disease. All of them were treated with benznidazol (5mg/kg/day) for one month; all of them presented anemia, which was interpreted to be an adverse drug reaction. The microhematocrit technique is believed to represent the best option for diagnosis of this disease in newborn children. A diagnostic methodology to follow the course of the infection is proposed.