A novel human cDNA (XPNPEPL) encoding a protein of 623 amino acids exhibiting 44% sequence identity and 62% sequence similarity to pig kidney X-prolyl aminopeptidase (aminopeptidase P; EC 3.4.11.9) was obtained by reverse transcription/polymerase chain reaction of phytohemagglutinin-stimulated lymphocyte mRNA. Conserved sequences were found with the prokaryotic X-prolyl aminopeptidase encoding gene (pepP). The human gene translation product exhibits a high sequence homology to the Schizosaccharomyces pombe chromosome I hypothetical protein C22G7.01c and to the S. cerevisiae ORF y11029w. Northern blot analysis indicates an ubiquitous expression of the human XPNPEPL sequence.