The various physiologic factors which might influence the time of first meconium passage were studied in 62 healthy full-term newborn infants. Thirty-two babies were born vaginally and 30 by elective cesarean section. Infants born vaginally were more acidotic and passed first stool earlier compared to those born by cesarean section. The same applies to vaginally delivered babies when comparing babies born to primipara and others. Acidosis is a presumed mechanism, and a role of gastrointestinal hormones is suggested to be the possible mediator of increased motility in these babies.