Fifty children with Hemophilus influenzae meningitis have been enrolled in a prospective study. Patients were randomly assigned chloramphenicol or ampicillin treatment; there were no significant differences between groups in other respects. Countercurrent immunoelectrophoresis proved to be a valuable tool for rapid diagnosis of the causative agent even in pretreated patients. Increasing, quantities of capsular polyribosephosphate antigen detected in the initial cerebrospinal fluid correlated significantly (r= 0.62419; p<0.01) with early and late sequelae of meningitis. None of the patiens died. severe and persistent neurologic or intellectual deficits were noted in four (8%) of the children, and an additional 14 (28%) had IQ, scores between 70 and 90. The presence of bactericidal antibody in serm was not protective. Anti-PRP antibody generally was not present in acute serum specimens and irrespective of the quantity of antigenic stimulus provided by the disease was nondetectable in 21 of 24 children less than 17 months of age following recovery.