Meconium, an ether extract of meconium, and the major free fatty acids of meconium (palmitic, stearic, and oleic acids) were all found to increase the surface tension minimum of dog lung extract in a Wilhelmy balance. Each of these fractions was instilled into the lungs of dogs (15 experimental, eight saline solution controls), and cardiac output, venous and arterial blood gases, pulmonary, atrial, and systemic pressures, airway pressure, and static lung compliance were serially monitored for 2 hours. Mean airway pressure increased and static lung compliance decreased significantly in all of the experimental groups. Although arterial pH and PaCO2 and the various hemodynamic measurements did not change during the experiment, PaO2 decreased significantly and did not return to baseline in all experimental groups. Extracts from atelectatic portions of experimental dog lung had a surface tension minimum of greater than 20 dynes/cm, whereas airway foam had a surface tension minimum of less than 10 dynes/cm, suggesting that the free fatty acids of meconium are able to strip surfactant from the alveoli.