During a ten-year period, 61 infants with perforated necrotizing enterocolitis were managed by bowel resection, enterostomy, and intravenous antibiotics. Aerobic and anaerobic cultures were taken of venous blood, from the peritoneal cavity at operation, and of any subsequent wound and/or intraperitoneal infection. No significant differences between fatal and nonfatal cases were noted with respect to presence of anaerobes in the peritoneal flora (six babies with two deaths) or culture-confirmed bacteremia (73% of the total). However, peritonitis participated in by Pseudomonas aeruginosa (ten babies), or beta-hemolytic streptococcus (five babies) was -niformly lethal, as were complicating bacteremias due to P aeruginosa, beta-hemolytic streptococcus, and Staphylococcus aureus (two each). Anaerobic peritoneal isolates (all gram-positive cocci) were never noted if performation occurred before the eighth day of life; they did not appear to adversely affect survival. Based upon these data, antibiotic therapy should include either gentamicin or tobramycin, with penicillin, until subsequent culture reports dictate otherwise.