We describe 2 sisters who presented with the hemolytic uremic syndrome (HUS) almost simultaneously. In both patients an upper airway infection with Haemophilus influenzae immediately preceding HUS may have been the environmental trigger. Fresh plasma infusion had only minor therapeutic effects but plasma exchange was followed by hematological remissions. One patient stayed dialysis dependent, the other had slow recovery of renal function on prolonged plasma exchange. These case histories suggest that in genetically predisposed patients HUS can be triggered by an infection with H. influenzae. Furthermore, when there is a poor response to plasma infusion recovery may be accelerated by plasma exchange