ESCHERICHIA COLI rarely produces purulent meningitis in man. Most cares reported in the literature are associated either with overwhelming E coli infections in infants and young children, or with congenital defects in the structures surrounding the spinal cord.1-7 In adults this infection is usually secondary to trauma to the central nervous system (CNS).8-10 Accordingly, the observation of two cases of E coli meningitis, one in a diabetic woman occurring in the setting of diarrhea and a urinary-tract infection, and the other in a woman with an asymptomatic urinary-tract infection, offered the opportunity to assess the possible responsible factors, and to review current concepts of the pathogenesis of E coli infections. Particular attention will be given to serogrouping of E coli, so-called pathogenic E coli, antibody response to infection, and the role of serum complement and diabetes. A review of the experience with E coli meningitis at the University