Leukocyte infiltration is a cardinal feature of almost all cancers. Chemokines are generally responsible for eliciting local accumulation of inflammatory cells and they appear to play the same role in the formation of peri- and intra-tumoural infiltrates. Chronic inflammation predisposes to cancer formation and progression, and it is likely that the chemokine system contributes to this process. In part, this may be a consequence of its ability to attract mononuclear cells to cancer sites, where they provide growth or angiogenic factors that enhance cancer development. However, accumulating evidence also points to a direct effect of chemokines on cancer cells that express chemokine receptors. In particular, some chemokines can activate anti-apoptotic pathways in these cells. By either mechanism, tumour cells that secrete and/or respond to chemokines would have a selective advantage. This provides another example of cancer's ability to co-opt host systems in order to promote tumour progression.