We have cloned and sequenced cDNAs encoding a mouse RNA-binding protein that is homologous to human HuD antigen. The amino acid sequence deduced from the nucleotide sequence has revealed that the mouse HuD protein is identical to the human counterpart except for two amino-acid substitutions outside the three RNA recognition motifs (RRMs) and a difference in the N-terminus. The mouse HuD gene produces two major brain-specific mRNAs (3.7 kb and 4.4 kb) and a minor testis-specific mRNA (1.3 kb), which is indicative of alternative RNA processing. These results suggest that the mouse HuD homolog is a member of the tissue-specific RNA-binding protein family, possibly involved in RNA metabolism in the nervous system.