Twenty-six adults with acute bacterial meningitis were enrolled in an open randomized comparative study. The organisms isolated from CSF were Streptococcus pneumoniae, Staphylococcus epidermidis, Haemophilus influenzae, Escherichia coli and Salmonella typhi. 13 patients (group A) were treated once daily with intravenous ceftriaxone (Rocephin®). The 13 patients in group B received ampicillin or ampicillin plus chloramphenicol in 4 doses/day. The mean duration of therapy in groups A and B was 9.9 and 12.3 days, respectively. This difference in the duration of therapy was statistically significant. All patients from group A showed clinical improvement and all were bacteriologically cured. In group B only 12 patients were clinically and bacteriologically cured; 1 patient had to be withdrawn from the therapy because CSF culture remained positive after 48 h of therapy. Ceftriaxone was well tolerated in all patients; ampicillin or ampicillin plus chloramphenicol were associated with diarrhea and skin rash in 6 patients.