This chapter shows that the rat a2-M promoter is regulated by a type II element binding a nuclear factor, which is rapidly activated by a posttranslational mechanism after the action of interleukin (IL)-6 or leukemia inhibitory factor. The sequences of the double-stranded oligonucleotides used in gel retardation assays are shown. The motifs matching the Acute Phase Response Factor (APRF) binding consensus are underlined. The sequences given in capital letters correspond to rat a2-M (core, core tandem, core-like, short core-like, and rat Acute Phase Response Element (APRE)), human a2-M (human APRE), rat a1-acid glycoprotein (AGP C), and C-reactive protein (CRPa) promoter sequences, respectively.