Background: We evaluated the effect of surfactant on platelet function as a potential contributing mechanism to the pathogenesis of pulmonary hemorrhage (PHEM) in term and preterm infants. Methods: Cord blood samples were collected from neonates following delivery. Complete blood count and platelet function were measured using a cone and platelet analyzer (CPA). Increasing surfactant concentrations were added to platelets in vitro, and the adhesion molecule P-selectin and the monoclonal antibody PAC-1 were evaluated following platelet activation by flow cytometry. Results: Forty-one infants (11 preterm and 30 term) were studied. CPA revealed a significant decrease in the average size of the aggregates and in platelet adhesion when surfactant was added. In term infants, the addition of surfactant to native platelets yielded an increased binding capacity of PAC-1 but did not affect P-selectin expression. In preterm infants, platelet activation with adenosine diphosphate in the presence of a high surfactant concentration (0.5 mg/mL) resulted in increased PAC-1 binding and no change in P-selectin expression. Conclusions: The platelets of preterm infants are less active (hyporesponsive) than those of term infants, both in their native state as well as after stimulation with various agonists. Surfactant may play an important role in treating PHEM in preterm infants.