Glycine significantly increases the MG-63 cell proliferation in a dosedependent manner. Activity of alkaline phosphatase (ALP) and phosphorylation of extracellular-signal-regulated kinase are increased by glycine in MG-63 cells. Glycine also increases the BrdU-incorporation and Ki-67 mRNA expression in MCF-7 cells, induces the up-regulation of estrogen receptor-β mRNA expression and estrogen response element-luciferase activity in MG-63 and MCF-7 cells.