The cDNA for human platelet-activating factor acetylhydrolase (PAF-AH) beta-subunit was cloned. The complete amino acid sequence deduced from cDNA contains 229 amino acids and is completely identical with that of the bovine subunit. Moreover, the sequence of the human beta-subunit protein shows 62.4% identity with the human gamma-subunit at the amino acid level. Southern blot analysis suggested the presence of multiple genes and we indeed found another closely related pseudo gene. Northern blot analysis showed that the 4.0 kb transcript was expressed in all tissues tested, suggesting the ubiquitous distribution of the subunit protein. Differential distribution of beta- and gamma-subunits might suggest that the oligomeric structure of PAF-AH is different from tissue to tissue.