The pig counterpart of human IHRP has been isolated from pig serum, and cDNA clones encoding this counterpart were isolated and characterized. The amino acid sequence of pig IHRP predicted from the nucleotide sequence of its cDNA shows reasonable homology to that of human IHRP. The nucleotide sequence of pig IHRP cDNA is identical to that of the mRNA partially determined to be the heavy chain of pig ITI [Buchman et al. (1990) Surgery 108, 560-566]; it is one of the major mRNAs induced in pig liver on cardiogenic shock. Thus we concluded that the reported mRNA should code for IHRP and not for the heavy chain of ITI. The pig IHRP also seems to be identical to pig-MAP, which was recently reported to be a major acute phase serum protein in pig [Gonzalez-Roman et al. (1995) FEBS Lett. 371, 227-230]. The results suggest that IHRP might be involved in acute phase reactions.