Twenty pregnant rabbits were studied in pairs. Half were given cortisol subcutaneously on days 24, 25, and 26 of gestation in dosage of 2 mg/kg/day. Half served as controls and received saline. The fetal lungs were studied on the 27th day of gestation by incubating lung slices in the presence of [6-14C]glucose. Glucose consumption significantly increased in the tissue from animals treated with cortisol, 17.61 "/- 5.56 (SD) mumol/g in the controls (P less than 0.05). The glycogen content of tissue treated with cortisol was significantly reduced compared to the controls, 2.42 +/- 0.97 (SD) mg/g wet lung versus 3.81 +/- 1.05 (SD) mg/g (P less than 0.05). Treatment with cortisol resulted in significantly enhanced incorporation of the 14C label into glycogen and phosphatidyl choline (Tables 3 and 4). These data suggest that glucocorticoids affect fetal lung phosphatidyl choline production by promoting glycogenolysis and increasing glucose incorporation into phosphatidyl choline.