Aim Monocyte chemoattractant protein-1 (MCP-1) plays an important role in migration of monocytes into subendothelial space. The purpose of this study is to examine whether thrombin and lipopolysaccharide (LPS) induce expression of MCP-1 mRNA and protein in calf aortic smooth muscle cells (SMCs). Methods Calf aortic SMCs were cultured by a substrate-attached explant method. The SMCs at the third to fifth passage which became confluent were used for the experiment. After a four-hour exposure to 2 ku/L thrombin and 100 μg/L LPS respectively, total RNA of SMCs of different groups were extracted by guanidinium isothiocyanate method. On the other hand, the SMCs of different groups after exposed to the above-mentioned inducers for 24 h, respectively, the conditioned media were collected. The expression of MCP-1 mRNA in SMCs was examined by dot blot analysis using a probe of γ- 32 P-labelled 35 mer oligonucleotide, and the MCP-1 protein in the conditioned media was determined by sandwich ELISA. Results Dot blot analysis showed that cultured SMCs were able to express MCP-1 mRNA at a low level. A 4 h exposure of SMCs to LPS and thrombin, respectively, induced a 1.6-fold and 2.1-fold increase in MCP-1 mRNA expression in the cells. After a 24 h exposure to thrombin, ELISA showed that the MCP-1 protein content in the conditioned media were also markedly increased (1.4-fold,P<0.05), while the MCP-1 protein content was not significantly increased (1.1-fold, P>0.05) after exposed to LPS for 24 h. Conclusions Thrombin is able to induce expression of MCP-1 mRNA and protein in cultured SMCs. It suggests that thrombin may play an important role in atherogenesis through increasing recruitment of monocytes in the arterial intima. The effect of LPS on the expression of MCP-1 in SMCs, hovever, is equivocal.