Physiologic changes associated with endotracheal intubation were examined in 10 preterm infants. Laryngoscopy was associated with apnea and minor abnormalities in cardiac rhythm in 2 infants. Three infants had nasal airflow recordings which demonstrated obstructed breaths during laryngoscopy. Systolic blood pressure (BP) increased 47% when the trachea was intubated, whereas heart rate and transcutaneous oxygen tension (PtcO2) decreased. Because endotracheal intubation is a physiologically stressful procedure, personnel who intubate preterm infants must be skilled and experienced to minimize the duration of laryngoscopy and the number of intubation attempts.