Liver mRNA levels of two acute phase reactant (APR) proteins, %-HS glycoprotein (a major negative APR) and q-acid glycoprotein (a major positive APR) were measured in male rats at different times after the administration of turpentine, of tumor necrosis factor, or following partial hepatectomy. In every case, a marked decrease in mRNA levels of a;-HS glycoprotein was observed which reached a maximum at 24 h. A concomitant increase of q-acid glycoprotein mRNA levels was observed under the same conditions. These results indicate that the decreasedlevels of d;-HS glycoprotein induced by the acute-phase response following inflammatory mediators and partial hepatectomy are due to a down-regulation of the gene expression of this protein in rat liver.