Using cDNA cloning, we have identified a new member of the gro/KC inflammatory protein superfamily (gro-beta) produced by activated human monocytes and neutrophils and expressed at sites of inflammation in vivo. The open reading frame encodes a protein with 91% sequence homology to the human gro protein. Interestingly, some of the amino acid substitutions are located at regions where proteolytic cleavage occurs in the gro protein generating biologically active peptides (neutrophil activating peptide III). These changes would likely alter the processing of the gro-beta peptide and suggest that peptides with biological activities different from those produced by gro-alpha are encoded by this transcript.