An interferon-inducible cytokine, IP-10, containing homology to a family of proteins having chemotactic (platelet factor 4, beta-thromboglobulin) and mitogenic (connective tissue-activating peptide III) activities has been mapped to chromosome 4 at band q21, a locus associated with an acute monocytic/B-lymphocyte lineage leukemia that exhibits the nonrandom translocation t(4;11)(q21;q23).