The cerebellum-specific hexadecapeptide, cerebellin, is derived from a larger precursor, precerebellin, that has sequence homology to the complement component C1qB. We report the cloning of the murine homolog of precerebellin, Cbln1, and a closely related gene, Cbln2. Amino acid comparison of Cbln1 with Cbln2 revealed that Cbln2 is 88% identical to the carboxy terminal region of Cbln1. That these are independent genes was confirmed by Southern analysis and genome mapping. Cbln1 was positioned to the central region of mouse chromosome 8, 2.3 cM distal of JunB and 6.0 cM proximal of Mt1, while Cbln2 mapped to the distal end of mouse chromosome 18, 1.7 cM telomeric of Mbp.