We conducted a prospective, randomized evaluation of oral chloramphenicol administration for completion of therapy of Haemophilus influenza type b meningitis in 44 children: 21 received drug by this route after the second day of therapy, the remainder continued to receive the drug intravenously. Resolution of clinical manifestations and cerebrospinal fluid indicators of meningitis was equivalent with both routes in 43 patients. One infant failed to achieve efficacious serum concentrations by either route of administration. Paired analysis of the area under the serum concentration versus time curve in 13 patients after oral and intravenous administration indicated equivalent bioavailability. Neutropenia was the only observed drug-related toxicity and correlated with the highest observed serum concentration. We conclude that: (1) chloramphenicol can be used by the oral route to complete treatment of H. influenzae type b meningitis; (2) a dose of 75 mg/kg/day is effective and less likely than higher doses to cause neutropenia; and (3) the measurement of serum chloramphenicol concentrations is important, regardless of route of administration.