This prospective study compared the coordination of sucking, swallowing, and breathing and its relationship to oxygen saturation in infants during breast-feeding and bottle-feeding. After 4 to 6 wk of exclusive breast-feeding, infants began bottle-feedings of expressed human milk using one of two systems: a soft-walled bottle and nipple (system 1, Playtex) or a hard-walled bottle and nipple (system 2, Avent). Infants' sucking, swallowing, breathing, and oxygenation were measured during breast-feeding and bottle-feeding, and coordination of these activities during breast-feeding and bottle-feeding were compared. During breast-feeding, swallowing occurred nonrandomly between breaths and did not interfere with breathing. The same distribution of swallowing occurred in infants fed with system 1, while swallowing occurred randomly in infants fed with system 2. Swallowing significantly increased during bottle-feeding among infants using system 2, but decreased among infants using system 1. Infants using system 2 also had a greater instability in the coordination of sucking, swallowing, and breathing and more perturbation of breathing. Oxygen saturation was significantly higher in infants fed with system 1 compared with system 2. These results suggest that the overall feeding pattern and oxygenation of system 1 are closer to the physiologic norm than system 2.