From January 1, 1969 to December 31, 1974, 98,446 patients were admitted to Ben Taub General Hospital, one of the Harris County District Hospitals and a major teaching institution for Baylor College of Medicine. Spinal fluid specimens from 17,638 (17.9%) patients were cultured, and 787 (4.5%) cultures were positive for pathogenic microorganisms. Haemophilus influenzae, type B, was most frequently isolated (23.8%), followed by Streptococcus pneumoniae (16.0%), Staphylococcus aureus (9%), Neisseria meningitidis (7.3%), and Enterococcus (7.3%). Previous studies have indicated that more than 70% of all the septic meningeal infections are caused by H. influenzae, meningococcus and pneumococcus. At this hospital these organisms were isolated from 47% of the specimens studied, indicating a changing pattern in the etiology of purulent meningitis. Although pediatric patients constituted only 11.5% of the admissions, 58.4% of the pathogenic microorganisms were cultured from these patients.