We have examined changes in translatable liver mRNAs during the acute phase response in several inbred mouse strains. Induction of mRNAs for the known acute phase reactants serum amyloid A, hemopexin, haptoglobin, and alpha 1-acid glycoprotein was observed. Two alpha 1-acid glycoproteins, termed AGP-1 and AGP-2, differing in size and charge, were found in all mice and appear to derive from distinct yet closely related mRNAs. Polymorphism in the structure of AGP-1 among strains was used to map the structural gene, Agp-1, to chromosome 4 near the b locus. Structural variation for serum amyloid A enabled mapping its structural gene, S alpha alpha, to chromosome 7, near Gpi-1. A wild-derived population of mice, Mus spretus, contains several variations of interest, including structural variations in many acute phase proteins and a putative regulatory variation specific to AGP-1. Further analysis of these genetic variants should provide novel insights into the acute phase response and the factors that mediate it.