Interleukin-1 receptor-associated-kinases (IRAKs) are signal transduction mediators of the Toll/IL-1 receptor family, which comprise several transmembrane proteins involved in host defense mechanisms. Today four different human IRAKs (hu-IRAK-1, hu-IRAK-2, hu-IRAK-M, hu-IRAK-4) and two murine IRAKs (mouse pelle like kinase (mPLK) and mu-IRAK-4) have been described. Here we report the identification and characterization of murine IRAK-M (mu-IRAK-M), a mouse homologue to human IRAK-M (hu-IRAK-M). These IRAK-M molecules show 71% sequence identity, a comparable cellular expression, and functional similarities with respect to signal transduction capacity and kinase activity, suggesting functional homology in signalling in human and mouse cells. (C) 2002 Elsevier Science (USA). All rights reserved.