TA Surfactant is a bovine surfactant that has been developed, tested, and used in over 30 infants with Respiratory Distress Syndrome in Japan by Drs. T. Fujiwara, Y. Tanaka, and colleagues. It is manufactured on a pilot basis by Tokyo Tanabe Co. in Tokyo. In preparation for further clinical trials, we have measured several characteristics of the surfactant. The material contains 83-90% (by weight) phospholipid, of which 69% is phosphatidylcholine (PC), 10% sphingomyelin, 7% phosphatidylethanolamine, and lesser amounts of other phospholipids. Approximately 85% of esterified fatty acids in PC are saturated. Qualitative analysis indicates the presence of free fatty acids, triglycerides, and a trace of cholesterol. Protein represents 1-3% of dry weight. Surface adsorption rates and measures of minimal surface tension equal values obtained for mammalian lung surfactants. Surfactant, sonicated in 0.9% sodium chloride (33 mg/ml), was instilled into adult rats (100 mg/Kg), that had been lavaged to remove endogenous surfactant. In all treated rats (n=6) prompt increases in serial PaO2 were noted. Static pressure volume characteristics indicated increased compliance in the treated group vs controls. Electron microscopic studies of pelleted TA Surfactant show vesicles, stacked membranes, and amorphous material. These studies indicate this substance should be an efficacious exogenous surfactant.