A family consisting of at least ten distinct novel 8-10 kd cytokines has been identified over the past 12 years. These cytokines exhibit from 20 to 45% homology in amino acid sequence, are probably all basic heparin-binding polypeptides, and have proinflammatory and reparative activities. The cDNA for these cytokines are characterized by conserved single open reading frames, typical signal sequences in the 5' region, and AT rich sequences in the 3' untranslated regions. Those human cytokines known as interleukin 8, platelet factor 4, beta thromboglobulin, IP-10 and melanoma growth stimulating factor or GRO can be assigned to a subfamily based on their location on chromosome 4 and unique structural features, whereas the second subset consisting of LD78, ACT-2, I-309, RANTES, and macrophage chemotactic and activating factor (MCAF) are all closely linked on human chromosome 17. In this review we have summarized and discussed the available information concerning the regulation and structure of the genes, the structure and biochemical properties of the polypeptide products, their receptors, signal transduction, cell sources, and in vitro as well as in vivo activities of these cytokines.