The hemolytic-uremic syndrome, although clearly described from the clinical and morphological points of view, has uncertain etilogy and pathogenesis for which various hypotheses have been advanced. In the immunohistochemical study of three recent infantile cases, whose clinical description and analysis follow those described in the literature, we found fibrinogen deposits, C3 and immunoglobulins in the walls and glomerular capillary vessels in two from which biopsies were taken early; while in the third case, in which the biopsy was taken a month after the process had begun, only fibrinogen was found. These findings suggest a pathogenesis of lesions involving an immunocomplex reaction with ulterior development of secondary intravascular coagulation. On the other hand, the presence or absence of C3 and immunoglobulins could be related to the timing of the biopsy, disappearing in the more developed cases. In the ultrastructural study performed in one of the case, besides other lesions habitually referred to, the presence of virus-like particles in the glomerular capillary endothelium was observed. Although having been seen in multiple locations and circumstances, this has not previously been described in the hemolytic-uremic syndrome, and it probably represents the morphological expression of degenerative glomerular processes.