A novel cyclosporin A binding glycoprotein of 21 kDa was isolated from human milk by several steps of cation exchange chromatography. The corresponding gene was cloned from human T cells, expressed in Escherichia coli and the recombinant protein purified. The protein shares 58% amino acid identity with the cytosolic cyclophilin and is initially synthesized with a hydrophobic leader sequence. The cyclophilin-like protein has also peptidyl-prolyl cis/trans-isomerase activity, although less efficient, that is inhibited by cyclosporin A. The existence of a secreted form of cyclophilin-like protein in addition to the previously known cytosolic cyclophilin implies that these proteins act on different in vivo targets.