Mitogen-activated protein (MAP) kinases comprise a family of conserved, eukaryotic enzymes that mediate responses to a wide variety of extracellular stimuli. We have identified a new human MAP kinase gene here termed BMK1. BMK1 encodes a protein of 816 amino acid residues and has at least three different forms of mRNA. BMK1 messages are abundant in heart, placenta and kidney but not detectable in liver. Although BMK1 has the dual phosphorylation site of MAP kinases characterized by the TEY sequence found in ERK1 and ERK2, it has a distinct C-terminal and loop-12 structure when compared to other mammalian MAP kinases. This suggests BMK1 may regulate signaling events distinct from those controlled by the ERK group of enzymes.