- Background Pulmonary hemorrhage (PHEM) complicates the hospital course of 3-5% of preterm infants with respiratory distress syndrome (RDS), and bears a high mortality rate. Impaired thrombin generation and poor clot formation in premature neonates affect PHEM severity. Objectives We evaluated the impact of surfactant upon in-vitro clot formation in order to assess the role of surfactant in the pathogenesis of PHEM. Methods Blood samples were obtained from healthy volunteers for measuring complete blood count, PT, PTT, and platelet function. Surfactant at increasing concentrations was added to blood samples, and whole blood clotting assays were performed using rotation thromboelastogram (ROTEM®, Pentapharm Munich, Germany) and whole blood platelet adhesion and aggregation (Impact-R®, Diamed, Switzerland). Results The mean PT level increased from 10.05 ± 033 to 11.64 ± 0.85 sec (p = 0.06) in the presence of surfactant. Platelet aggregation with the agonists adenosine diphosphate and epinephrine significantly decreased with escalating surfactant concentration (p < 0.001). Adhesion, manifested by surface coverage (SC), significantly decreased with increasing surfactant concentration: mean SC 9.25 ± 2.96 compared to 6.1 ± 0.96 and 0.05 ± 0.058 with 0/0.1/5 mg/ml surfactant, respectively, p < 0.001 Whole blood ROTEM studies showed a trend towards lengthening of clotting time with increased surfactant concentration and lower clot strength. Conclusion The presence of surfactant impairs coagulation in-vitro. The risk of PHEM may therefore be greater in extremely premature infants. Future studies are required to assess the clinical significance and relevance of our preliminary findings.