The GRO gene was originally identified by subtractive hybridization studies between normal and tumorigenic Chinese hamster embryo fibroblasts. The hamster cDNA was cloned and used as a probe for cloning of the human GRO cDNA. The GROalpha gene initially cloned from T24 cells and the gene in melanoma cells encoding melanoma growth stimulating protein (MGSA) are identical. Human cells contain three closely related, but distinct GRO genes: GRO alpha, GRO beta, and GRO gamma. GRO beta and GRO gamma share 93% and 82% identity, respectively, with GRO alpha at the nucleotide level. GROs are members of the chemokine alpha family that is characterized by the separation with one amino acid of the first two cysteine residues, C-X-C, in the amino acid sequence. The GRO gene has been mapped to chromosome 4q21. In normal cells, human mRNA GRO expression is found in foreskin fibroblasts, synovial fibroblasts, chondrocytes and osteocytes. Additionally, GRO mRNA has been detected in mammary fibroblasts, mammary epithelial cells, endothelial cells, activated monocytes, macrophages, and neutrophils. Characterization of the GROalpha receptor indicates the presence of low and high affinity receptors on human neutrophils.