Sixty consecutive wound infections were studied among 1104 women undergoing cesarean section. Wound infections caused by cervical-vaginal flora were associated with prolonged labor, particularly with greater duration of fetal monitoring and number of vaginal examinations, and with organisms isolated from the endometrium at cesarean section. In contrast, women with wound infections caused by Staphylococcus aureus had neither prolonged labor nor S aureus isolated at cesarean section. The 25% of wound infections associated with S aureus represent potentially preventable conditions that presumably arise from exogenous sources.