ObjectiveTo find out if hepatocyte growth factor (HGF) in amniotic fluid (HGF-AF) has a direct effect on fetal lung development, we investigated the effects of AF as well as recombinant human HGF (rhHGF) on proliferation, migration, and morphogenesis of fetal alveolar type II cells in vitro.MethodsAmniotic fluid samples were obtained from 37 women at various gestational ages. Mitogenic, motogenic, and morphogenic activity was investigated by 5-bromo-2′deoxyuridine incorporation, Boyden chamber assay, and culture in collagen-gels, respectively.ResultsThe motility of AK-D cells was stimulated by AF from 14 to 31 weeks' gestation in proportion to the concentration of HGF-AF, and this effect was comparable to that observed with rhHGF. Furthermore, this activity was neutralized by anti-human HGF antibody. However, AF samples subsequent to 32 weeks had no motogenic influence despite the continued presence of immunoreactive HGF-AF. Neither increased DNA synthesis nor morphogenesis in response to AF was identified under the conditions used.ConclusionThe present study suggests that AF stimulates alveolar type II cell migration by way of HGF-AF in vitro.