Nine cases of the hemolytic-uremic syndrome and one case of purpura fulminans were studied clinically and virologically. All were thought to represent examples of varying degrees of intravascular coagulation. Virological studies demonstrated a high frequency of infections with enteroviruses, particularly Coxsackie viruses. Evidence of such infections was found in 7 of the 10 subjects, and similar viral Infections were found among family contacts of 5 of the subjects. Studies of the various subjects and the available family contacts demonstrated evidence of having recent enteroviral infection in the patient and/or the immediate family in 9 of the 10 subjects studied. It is suggested that enteroviruses may have a role in initiating the sequence of events involved in the pathogenesis of these illnesses.