The influence of terbutaline on content of phospholipids and their fatty acid composition in fetal lung wash and lung homogenates was studied in 28-day-old rabbit fetuses. To obtain both the fatty acid composition and the quantity of lecithin and sphin-gomyelin gas-liquid chromatography (GLC) was used, which gave a linear relationship when compared to standard solutions of the phospholipids. The amount of lecithin was significantly increased in the lung wash in terbutaline-treated fetuses compared to controls, while the sphingomyelin content was unchanged. In the lung homogenates no quantitative differences were noted between the two groups. The fatty acid composition of lecithin and sphingomyelin did not alter neither in lung wash nor in lung homogenate after terbutaline administration. The present results indicate that beta-mimetics mainly act by favouring the release of preformed surfactant and not by stimulating the synthetic capacity of type II cells in the alveolar lining layer.