We have cloned, sequenced and expressed a gene of Haemonchus contortus that encodes a protein (termed HcCYP) consisting of a cyclophilin domain and an RNA recognition motif (RRM). An antiserum raised against the recombinant protein showed that HcCYP was present in the insoluble fraction (mostly nuclear) of the parasite homogenate. The recombinant protein possessed the typical cis-trans peptidyl-prolyl isomerase activity of cyclophilins and this activity was inhibited by the immunosuppressant cyclosporin A. The N-terminal portion of the molecule, carrying the RRM, was able to bind to nucleic acids, whereas the C-terminal portion did not have any binding activity. The possible function of HcCYP in the parasite is discussed on the basis of information available on similar proteins in other organisms.