The recently isolated gene for neurofibromatosis type 2 (NF2) encodes a 595 amino acid protein, named merlin, which is related to the cytoskeleton-associated proteins moesin, ezrin and radixin. To identify evolutionarily conserved regions and to provide sequence information necessary for the establishment of a mouse model for NF2, we have determined the cDNA sequence of the mouse NF2 tumor suppressor gene, and mapped it in the mouse genome. Mouse merlin is a 596 amino acid protein, 98% identical to human merlin, but one amino acid longer due to the insertion of a proline residue near the C-terminus. Of the nine amino acid differences between mouse and humans, seven occur in the C-terminal 20% of the protein, far from the protein 4.1 domain that defines this family. Two of the NF2 cDNA clones reveal evidence of alternative splicing events that alter the predicted merlin product, one removing a 45 amino acid segment from the middle section of the protein and the other changing the C-terminus. The existence of several different forms of merlin potentially with different primary roles will complicate the identification of the precise function that must be disrupted to cause the NF2-associated tumors. The mouse NF2 homologue maps to Chr 11, in a region homologous to human Chr 22, but devoid of any mouse mutations which could be models of the human disorder.