A complementary DNA plasmid library has been constructed in the plasmid pUC19, using poly (A) containing RNA isolated from the frozen rat brain tissue as the starting material. Double stranded cDNA was inserted into the Eco RI site of the plasmid using Eco RI linker, then transformed into E. coli JM83. From the resulting 1,900 colonies 26 plasmids containing cDNA copies of the brain-specific mRNA were selected by in situ colony hybridization and southern hybridization using ss cDNA probe synthesized from the liver mRNA. These cDNAs were randomly subcloned and sequenced. tight subclones were selected from the analysis of the deduced amino acid sequences carring dibasic amino acid sequence appeared intermittently. Five clones corresponding to eight subclones were isolated and partially sequenced.