The effects of dexamethasone on pulmonary de novo fatty acid synthesis were investigated in a fetal rabbit lung explant model. Culture of the explants for 2 or 6 days with dexamethasone produced a 48% increase in de novo fatty acid synthesis, measured by 3H2O incorporation, and a 2.5-fold increase in [3H-methyl] choline incorporation into phosphatidylcholine. A dose-response study showed this effect plateaued at dexamethasone concentrations above 10(-9) M. The distribution of the products of de novo fatty acid synthesis was altered by dexamethasone. Treated cultures had a 2.5-fold increase in esterification of the newly synthesized fatty acids to phosphatidylcholine and an increase in the proportion of all newly synthesized fatty acids that were used for phosphatidylcholine synthesis. Dexamethasone treatment significantly increased the total fatty acid content and the phosphatidylcholine fatty acid content of the explants by 27 and 85%, respectively. The newly synthesized fatty acids were esterified almost equally to the 1 and 2 positions of phosphatidylcholine; this distribution was not altered by dexamethasone. These studies demonstrate that fatty acid synthesis and distribution are regulated in the fetal lung, at least in part, by glucocorticoids. In addition, coordinate regulation of fetal lung de novo fatty acid synthesis and surfactant phosphatidylcholine production by glucocorticoids is likely.