Fifty consecutive patients with meningococcal meningitis aged 7 to 75 years (mean, 29 years) were treated with intravenous penicillin G sodium (2 to 3 X 10(5) U/kg/d) for four days. Two of the patients (both teenagers) died of fulminant infection during the first 36 hours of therapy and one elderly woman developed aspiration pneumonia requiring penicillin therapy to be prolonged beyond four days. The remaining 47 patients recovered from the infection. On the fourth day, fever, mild meningeal signs, and moderate elevations of cerebrospinal fluid cell counts and protein contents persisted in some patients; nevertheless, all patients were cured without relapse. The results of our study suggest that meningococcal meningitis may be successfully treated with a four-day course of intravenous penicillin G.