Crystal-cell interactions play a key role in the formation of kidney stones. Few studies have referred to the role of monocyte chemoattractant protein-1 (MCP-1) and transforming growth factor beta 1 (TGF beta 1) in kidney stone formation. Recently, a genome-wide analysis of genes related to kidney stone formation and eliminiation in mice indicated that MCP-1 and TGF beta 1 are involved in nephrolithiasis. In this study, in order to verify whether MCP-1 and TGF beta 1 are involved in the process of crystal-cell interactions in vitro, we observed the effects of calcium oxalate monohydrate (COM) on MCP-1 and TGF beta 1 expression in cultured HK-2 cells. HK-2 cells were treated with different concentrations of COM, and a group of untreated cells served as the control. The expression of MCP-1 and TGF beta 1 was detected by western blot analysis after treatments with different COM concentrations (300, 500, 700 and 900 mu g/ml for different times (3, 6, 12 and 24 h). We found that the expression of MCP-1 was upregulated by COM treatment in a dose-dependent manner, and was increased initially at the first 6 h of treatment, then slightly decreased over time. Also, COM treatment resulted in a dose-dependent increase in TGF beta 1 expression, and the expression levels peaked at 12 h. This study demonstrates that COM stimulates the expression of MCP-1 and TGF beta 1 in renal epithelial cells.