BACKGROUND: Although several growth factors are known to be essential for liver regeneration, the role of gastrin remains controversial. METHODS: Liver regeneration was examined in wild-type (WT) and gastrin-deficient (gastrin KO) mice at days 2 and 10 after partial (40 ) hepatectomy by measurement of liver weight. Hepatocyte proliferation and circulating gastrin concentrations were measured at the same time points by immunohistochemistry and radioimmunoassay, respectively. RESULTS: There was no significant difference in the rate of liver regeneration between gastrin KO and WT mice. Hepatocyte proliferation in both groups was increased at day 2 but had returned to baseline values by day 10. At day 2, hepatocyte proliferation in the gastrin KO mice was significantly higher than in WT animals, whereas at day 10, proliferation was significantly greater in the WT mice. The circulating gastrin concentration in the WT mice was significantly lower at day 10 than in unoperated WT animals. CONCLUSION: This study suggests that gastrin is not essential for liver regeneration after partial hepatectomy.