Organ cultures were set up from human fetal lung originating from the first trimester of gestation (8-12 weeks) and followed their morphological differentiation in the absence and in the presence of Dexamethasone, Betamethasone, Ambroxol and Dexamethasone + Fenoterol. We were especially interested in studying whether multilamellar bodies and tubular myelin structures which are characteristic of the human surfactant, could be demonstrated in the cells after different treatment. Dexamethasone and Betamethasone promoted directly the development of the multilamellar bodies and the tubular myelin structures in the type II cells. - Furthermore, Ambroxol (Bromhexin-metabolite VIII) produced a prominent stimulatory effect in the synthesis of the surfactant in a concentration of 12 ng/ml. Fenoterol has probably no stimulatory effect on the surfactant production. In cultures treated with 10 ng/ml Fenoterol + 10 ng/ml Dexamethasone the benefit effect of Dexamethasone in stimulation of the multilamellar bodies was impaired. Our investigation shows that the human fetal lung is able to respond to the action of glucocorticoids and Ambroxol as early as in the first trimester of gestation by accumulating phospholipids.