Fibroblast-pneumonocyte factor (FPF) is an organ-specific differentiation factor produced, under glucocorticoid regulation, by the fetal lung fibroblast, which in turn enhances the differentiation of the alveolar type II cell with respect to surfactant production. In this article we review the appearance of the type II cell phenotype during fetal life and the action of FPF to time full acquisition of this phenotype. Evidence supporting a physiological role for this factor is reviewed as are details of its production by the fetal lung fibroblast and action on the type II cell. Finally we summarize possible future clinical advantages of using such a material to regulate lung maturation compared with currently used maternal glucocorticoid therapy. These include a more rapid effect and bypassing the inhibition of glucocorticoid action seen in male fetuses and in infants of diabetic mothers.