Three linked genes for the CXC-chemokine melanoma growth stimulatory activity/growth related protein (MGSA/GRO) have been previously characterized and mapped to chromosome 4q12-q13. We have isolated and characterized a pseudogene, MGSA/GRO delta, which is 83% similar to the MGSA/GRO alpha gene in the region spanning the 5' UTR, first and second exons, and the first intron. The 5' upstream sequence for the MGSA/GRO delta gene, which is also very similar to the MGSA/GRO alpha, beta, gamma genes, contains a conserved NF-kappa B motif, a TATA box, and a transcription initiation site. However, the sequence becomes markedly divergent after the second exon and hybridization studies indicate that sequences similar to the third and forth exons of other MGSA/GRO genes are not present in this gene. Additional sequence differences include alteration of the MGSA/GRO delta translation initiation codon and a one base insertion resulting in an apparent frame shift and early termination within exon 2. Multiple mutations such as these are characteristic of pseudogenes.