A cloned cDNA that encodes human reticulocyte 15-lipoxygenase was characterized by Northern blot analysis and heterologous expression in bacteria. The 2.7 kb cDNA specifically hybridizes to reticulocyte RNA from anemic rabbits. The RNA levels correlate with the appearance of enzymatic activity in anemia. The cDNA was subcloned into an inducible bacterial expression vector in frame with the amino terminal ten amino acids of beta-galactosidase (pUCLOX). The soluble fraction of the cell lysate of E. coli transformed with pUCLOX contained a protein that has the same catalytic and antigenic characteristics as reticulocyte 15-lipoxygenase.