We cloned two rat cDNAs of brain basic helix-loop-helix factor 1 (BHF1). These have an identical coding region, contain 357 amino acids and exhibit 94.6% identity to MATH-2/NEX1 in the basic helix-loop-helix region. BHF1mRNAs are dominantly expressed in the brain particularly in the cerebellum, in the adult bovine, rat and mouse. Two shorter BHF1mRNAs (1.6 kb and 1.8 kb) were also detected in the mouse embryo, and these decreased in the developmental process. These results suggest that BHF1 may play important roles in cerebellum-specific functions and development of neurons.