T-kininogen plays an important role in the acute phase response to trauma in the rat as a possible source of kinins and as a cysteine proteinase inhibitor. Two T-kininogens are expressed by rat liver from two separate genes. T-kininogen expression in liver during the acute phase response is regulated at the level of transcription. The similarity in T- and K-kininogen gene structure suggests divergent evolution from a common gene ancestor.