The preferential screening of cDNA libraries derived from the mouse osteoblastic cell line MC3T3-E1 has yielded a cDNA clone encoding 796 amino acids including the typical 24-residue-long signal sequence. The predicted amino acid sequence revealed that this protein constitutes a new member of the cadherin family. We propose the name OB-cadherin (OB for osteoblast) for this new protein. RNA analyses revealed that the OB-cadherin gene is selectively expressed in osteoblastic cell lines, precursor cell lines of osteoblasts, and primary osteoblastic cells from calvaria, as well as in lung, testis, and brain tissues at low levels. Transfection of OB-cadherin cDNA into L cells resulted in the acquisition of the Ca(2+)-dependent adhesive property. Two different forms of the human OB-cadherin cDNA were subsequently cloned; one is a counterpart of mouse OB-cadherin gene, and the other encodes a protein with a truncated cytoplasmic domain. The results suggest that the newly found OB-cadherin might have an important role in bone formation.