It is becoming increasingly apparent that hepatocyte growth factor (HGF)1 plays an important role in kidney development, regeneration, and transformation to carcinoma. Previous in vitro studies have shown that HGF stimulates cell scattering, but not proliferation, in the renal epithelial cell line Madin-Darby canine kidney (MDCK) when grown on plastic at low density. This communication demonstrates that HGF treatment of confluent monolayers of MDCK also stimulates DNA synthesis and cell division. HGF stimulated thymidine incorporation in confluent MDCK cell monolayers grown on plastic in a dose dependent fashion, but did not stimulate thymidine incorporation in MDCK cells at 10-20% confluency on plastic. Additionally, basolaterally, but not apically, applied HGF stimulated thymidine incorporation in confluent MDCK cell monolayers grown on filters. Immunofluorescent labeling of nuclei in control and HGF treated MDCK cell monolayers grown on filters demonstrated an increase in mitotic figures. Confocal X-Z section views and direct cell counts of MDCK cell monolayers grown on filters demonstrated an increase in cell number after HGF treatment compared to controls. This is the first report of HGF stimulating cell proliferation in previously quiescent renal epithelial cell monolayers. This model will be useful for studying the mechanisms controlling cell proliferation rates in epithelial tissue.