Hypoxia promotes the invasive and metastatic potential of tumour cells. A recent study has shown that the activation of the chemokine receptor CXCR4 by lack of oxygen in breast cancer is HIF-1-dependent. We have previously demonstrated that CXCR4 signalling is involved in the establishment of lymph node metastasis in oral squamous cell carcinoma (OSCC). In this study, we investigated a correlation between CXCR4 and HIF-1alpha expression in OSCC. Immunohistochemistry showed that CXCR4 was expressed in 20 of 85 OSCC tissues, while HIF-1alpha was expressed in 51 of 85 samples. There was a significant correlation between the expression of CXCR4 and HIF-1alpha. In human OSCC cells, hypoxia markedly enhanced the expression of both HIF-1alpha and CXCR4. Furthermore, synthetic small interfering RNA specific for HIF-1alpha significantly suppressed the expression of this protein, and also attenuated the induction of CXCR4 expression under hypoxic conditions. These results indicated that HIF-1alpha regulated hypoxia-induced CXCR4 expression in OSCC.