BACKGROUND: There are few studies conceming morphological charactedstics, space-time distribution and differentiation of hepatic stem cells during embryo liver development.OBJECTIVE: To understand the action of alpha fetoprotein, cytokeratin-19 (CK19) and c-Met in the liver through observing the expression of them.DESIGN, TIME AND SETTING: The in vitro cytological observational study was performed at the Central Laboratory of Weifang Medical College from June 2005 to December 2006.MATERIALS: A total of 40 embryo samples were obtained from 3-rnonth aborted fetus, which were supplied by Hospital Affiliated to Weifang Medical College.METHODS: Aborted embryo was collected and made into sections within 30 minutes. Fetal age was defined according to embryonic layer formation, somite number and organ development under a microscope. Sample sections with fetal age of 3-12weeks were selected. One was collected from every eleven sections and underwent immunohistochemical staining.MAIN OUTCOME MEASURES: Expression of alpha fetoprotein, CK19 and c-Met was measured in embryo hepatic stem cells aged 3-12 weeks.RESULTS: At 3-5 weeks, samples were positive for alpha fetoprotein and c-Met, which were indicated as hepatic stem ceils. At 10-12 weeks, alpha fetoprotein- and c-Met-positive cells were mainly distributed surrounding the header, which suggested that hepatic stem cells were mainly located at hepatic cord of the header. This had similar distribution as adult hepatic oval cells (adult hepatic stem cells). CK19-positive reaction was found at week 7, and mainly at hepatic cord cells, bile duct sheet cells and bile duct epithelial cells at 10-11 weeks. CKlg-positive reaction was only seen at the bile duct sheet and bile duct epithelial cells at week 12. At this time, all bile duct sheet cells and bile duct epithelial cells were positive for alpha fetoprotein, c-Met and CK19.CONCLUSION: CK19-positive reaction was not found in hepatic stem cells, but only detected in bile duct epithelial cells and progenitor calls. CK19 may be not fit for a marker of hepatic stem cells. All bile duct sheet and bile duct epithelial cells are positive for alpha fetoprotein, c-Met and CK19. It is assumed that alpha fetoprotein+/c-Met+/CK19+ may be bile duct progenitor calls.