Although several studies have suggested that CXCL12 and its receptor, CXCR4, may play a role in embryo implantation, there are limited reports of expression of CXCR4 and CXCL12 in human endometrium. The aim of this study was to investigate CXCL12 and CXCR4 expression in human endometrium and to see if CXCL12 could affect matrix metalloproteinase (MMP) production by endometrial stromal and epithelial cells.Quantitative real-time RT-PCR (qRT-PCR) was used to detect the expression of CXCL12 and CXCR4 mRNA in endometrial biopsy samples obtained from fertile women (n = 30). Immunohistochemical analysis was carried out to determine where in the endometrium CXCL12 and CXCR4 were expressed. Primary cell culture followed by qRT-PCR and zymography was used to investigate whether CXCL12 affected MMP-2 and -9 production by endometrial stromal and epithelial cells.Both CXCL12 and CXCR4 were detected in the endometrium. There was no difference in CXCL12 expression at different times in the cycle, but expression of CXCR4 mRNA was significantly higher in the early proliferative (P < 0.01) compared with late proliferative and secretory phases of the cycle. CXCL12 expression was strongest in the epithelial compartment, and weaker in blood vessel walls. CXCR4 immunostaining was strong in the epithelium and blood vessel walls and weaker in the stroma. CXCL12 (10 and 100 ng/ml) had no effect on mRNA expression or activity of MMP-2 or MMP-9 in either stromal or epithelial cells.The results show that the expression of CXCL12 in human endometrium does not alter during the menstrual cycle, while the endometrial expression of its receptor, CXCR4, is highest in the early proliferative phase. In contrast to its effects in other cells, CXCL12 had no effect on MMP-2 or MMP-9 production by endometrial stromal or epithelial cells.