Two patients who lived in Buenos Aires suburbs died from leptospirosis in July 2000 and March 2001. They developed a nonspecific febrile illness followed by hemorrhagic pneumonia and respiratory distress in absence of typical manifestations such as jaundice, nephropathy, thrombocitopenia or hemorrhages in other organs. In the house and surroundings of one patient rodents were captured and three strains of leptospira, serogroup Icterohaemorrhagiae were isolated. Laboratory guinea pigs were inoculated and they were sacrificed as soon as respiratory symptoms appeared. Necropsy showed primary lung injury, which was similar to the histopathological lesions found in one of the patients. Neither jaundice, nor renal damage was found. Pericardiac hemorrhages were considered as a possible cause of cardiopulmonary collapse. This clinical form has not been reported previously in this region, where conditions are indeed suitable for the human illness to appear.