Macrophage inflammatory protein-1 alpha (MIP-1 alpha) belongs to the "chemokine" superfamily of chemoattractant pro-inflammatory cytokines. MIP-1 alpha is chemotactic for monocytes and neutrophils and thus, plays an important role in initiation and control of inflammation. We have isolated and sequenced a cDNA clone encoding rat MIP-1 alpha. This 0.75 kb cDNA includes a single open reading frame of 92 amino acids. Expression of MIP-1 alpha mRNA was characterized in NR8383, a rat alveolar macrophage cell line (RAM). In resting RAM cells, MIP-1 alpha mRNA decayed rapidly, with a half life of less than 2 hours. Lipopolysaccharide (LPS) treatment of RAM cells resulted in a dose-dependent increase in MIP-1 alpha steady state mRNA expression. The induction of MIP-1 alpha mRNA by LPS was partially the result of mRNA stabilization, as half life increased to over 6 hours.