Monocyte chemoattractant protein 1 (MCP-1) has been shown to be effective for the stimulation of collateral artery formation in small and large animal models. The availability of a genetic knockout mouse enables evaluation of the importance of the role of MCP-1 in the natural course of collateral artery growth. In a total of 21 MCP-1 -/- as well as 13 of the appropriate genetic background controls ([129Sv/J X C57BI/6J]F1), a femoral artery ligation was performed. Subsequently, a polyethylene catheter, connected to an osmotic minipump, was inserted retrogradely into the occluded femoral artery with the tip pointing upstream. Using this technique, PBS (MCP-1 -/-: n = 13 and C57BI/6J: n = 13) or MCP-1 (JE; MCP-1 -/-: n = 8) was delivered intra-arterially. Seven days after ligation, determination of hind limb flow was assessed by controlled tissue perfusion using differently labeled fluorescent microspheres. MCP-1 -/- mice exhibited a reduction of hind limb flow of 32.9 +/- 9.2% of the unligated hind limb, compared with 55.4 +/- 6.8% in C57BI/6J mice (p<0.01). MCP-1 -/- mice that underwent a subsequent 'rescue' treatment with MCP-1 showed a restoration of flow to a level of 47.4 +/- 9.8% (p = NS compared with PBS-treated C57BI/6J). Specific immunohistochemical staining for monocytes (MOMA-2: MCP-1 -/-, n = 5 and C57BI/6J, n = 5) showed a reduced number of monocytes around developing collateral arteries in the MCP-1 -/- mice. In conclusion, our data show that the absence of MCP-1 causes a strong reduction in flow restoration after femoral artery occlusion, coinciding with a reduced monocyte attraction, emphasizing the central role of this chemokine in the multifactorial process of collateral artery formation.