We cloned two kinds of cDNAs encoding novel Contactin/F3-subgroup adhesion molecules, which we termed NB-2 and NB-3. Nucleotide sequence analyses have shown that NB-2 and NB-3 are comprised of 1099 and 1028 amino acid residues, respectively. There was 51% similarity in the amino acid sequence of NB-2 and NB-3. NB-2 shared 46, 43, 55 and 55% identities with Contactin/F3, Tag-1, Big-1 and Big-2, respectively, at the amino acid sequence level. Likewise, the amino acid sequence of NB-3 exhibited 42, 44, 58 and 60% identities with Contactin/F3, Tag-1, Big-1 and Big-2, respectively. Expression of NB-2 mRNA was restricted to cerebrum, cerebellum and was hardly detectable, if any, in spinal cord. On the other hand, high expression of NB-3 mRNA was observed in spinal cord, as well as in cerebrum and cerebellum. In the other tissues, no expression of NB-2 and NB-3 mRNAs was detected.