In order to evaluate the clinical aspects of gram-negative bacillary meningitis (GNBM) we reviewed the charts of 20 adult patients with the discharge diagnosis of meningitis caused by gram-negative bacilli (bacteriologically proved) seen between 1973 and 1984. Nine patients had post-neurosurgical (post-NS) GNBM and 11 patients spontaneous (S) GNBM; the mean age of the former was 42 +/- 16 years and of the latter 56 +/- 14 years (p less than 0.05). The overall mortality rate was 50% (33% in the post-NS group and 64% in the S group). The glucose levels in CSF were significantly lower in the patients who died. Patients treated with combined aminoglycoside therapy presented a lower mortality rate than those treated with intravenous aminoglycoside only (25% versus 70%). We suggest that if aminoglycoside therapy is employed, these antibiotics must be administered both intravenously and directly into CNS.