We have isolated a near full-length cDNA encoding human leukotriene A4 hydrolase, which synthesizes a potent chemotactic and spasmogenic compound, leukotriene B4. A human spleen cDNA library was screened with a 48-mer oligonucleotide probe, synthesized according to the partial amino acid sequence of the human leukocyte enzyme. The nucleotide sequence of the cDNA had an open reading frame of 1,833 base pairs, which contained regions coding for the N-terminal amino acid sequence, the amino acid sequence for the probe design, and several other peptide sequences of the enzyme. The complete primary structure of the enzyme composed of 610 amino acid residues (molecular weight, 69,153) was deduced from the cDNA.