We describe the expression patterns and subcellular localisation of murine rel/NFκB transcription factors and their inhibitors during preimplantation development in the mouse. We find that the known rel and IκB proteins are ubiquitously expressed during early murine embryogenesis. The differential persistence of individual rel and IκB transcripts in the first cleavage stage embryo and analysis of the 3'UTR suggests that rel and IκB protein expression may be regulated at the level of mRNA stability and translation. At the stages of early mouse embryogenesis examined, there was no evidence for strong induction of rel dimer translocation into the nucleus. However, novel κB-binding proteins are found in the mouse blastocyst and may provide an alternative mechanism for regulation of gene expression via the κB motif in the early mouse embryo.