We isolated a human cDNA clone encoding a novel protein homologous to cyclophilins, specific cellular targets of cyclosporin A, which are conserved in species ranging from human to prokaryotes. This cDNA, designated hCyPX, contained an open reading frame of 498 nucleotides encoding 166 amino acids. Computer analysis indicated that its predicted amino acid sequence had 41.6%, 40.4%, and 39.2% homology to those of human, bovine, and Drosophila cyclophilins, respectively. Northern blot analysis indicated ubiquitous expression in adult human tissues, but most abundant expression in heart. Fluorescence in situ hybridization to human metaphase chromosomes localized this gene (PPIL1, peptidylprolyl isomerase [cyclophilin]-like 1) to chromosome bands 2p23.3-->p23.1.