The chemokine superfamily is a large group of small proteins, which share a limited amount of primary sequence identity, although a highly conserved three-dimensional subunit structure. The original members of the superfamily, Interleukin-8 and MCP-1 were purified over 10 years ago. Following on from these discoveries, many more of these proteins were identified because of their ability to selectively recruit and activate specific leukocyte populations. From these initial discoveries, the number of chemokines that have been discovered has increased almost exponentially in the last two years. Two main factors have been key to the discovery of so many new chemokines: first, the availability of large amounts of sequence information gained by random sequencing of cDNA libraries generating expressed sequence tag collections (ESTs); and second, the availability of this information on-line to research groups via the world wide web. This has meant the rapid increase in the number of chemokines that are currently well characterized. An additional spin-off of these novel chemokines is that a number of putative chemokine receptors have been paired up with their ligands over the last year.