mRNAs for low and high molecular weight kininogens (1.6 and 3.0 kb in size, respectively) and for two thiostatins (1.6 kb in size) were found in the liver of kininogen-deficient Brown-Norway (BN/Mai Pfd) rats. The levels of mRNAs for thiostatins, but not those for low and high molecular weight kininogens (arising from a single kininogen gene), increased strongly during acute inflammation. The pattern of DNA restriction sites for the kininogen gene and the thiostatin genes in the mutant rat strain was identical to that in at least four other rat strains.