Bacterial meningitis is not always easy to recognize clinically.1 Signs of meningeal irritation are often preceded by an upper respiratory infection, otitis media, or fever. Until they appear, meningitis may be unsuspected and antibiotic agents may be administered before a diagnostic lumbar puncture is performed. Exact information about such preliminary treatment is difficult to obtain. Consequently, little is known of the effects of such early therapy on the course of the disease. To evaluate the effect of preliminary antimicrobial therapy, the experience with bacterial meningitis at Wilford Hall USAF Hospital was reviewed. Inasmuch as the patients were seen at a military medical facility during the entire course of the disease, it was possible to reconstruct the early phases of the illness and to determine which patients had received antibiotic therapy before meningitis was recognized. Clinical Material Seventy patients with nontuberculous bacterial meningitis seen during the seven-year period from February