We studied 212 patients undergoing emergency cesarean section at an urban hospital. Four techniques of antibiotic prophylaxis were used, including single-dose and triple-dose parenteral therapy, parenteral and lavage therapy, and lavage therapy alone. One agent, mezlocillin, was used for all patients. There was no significant difference in surgically related infectious morbidity among the groups. This antibiotic proved efficacious when related to historical controls, and was the most economical of the modalities of administration studied.