14.3.3 protein, a brain-specific protein, is an activator of tyrosine and tryptophan hydroxylases, key enzymes for biosynthesis of dopamine and serotonin. In this article, we describe cloning of cDNA for human brain 14.3.3 eta chain and expression of 14.3.3 eta chain mRNA in some human cultured cells. The cloned cDNA is 1730 bp long and contains 191 bp of a 5'-noncoding region, the complete 738 bp of coding region, and 801 bp of a 3'-noncoding region, containing three polyadenylation signals. This cDNA encoded a polypeptide of 246 amino acids (M(r) 28,196). Furthermore, using in situ hybridization histochemistry, the expression of mRNA for this protein was examined in the rat central nervous system. In situ hybridization histochemistry indicated that 14.3.3 eta chain mRNA is detected not only in the monoamine-synthetic neurons, but also in other neurons in the discrete nuclei, which synthesize neither cathecholamine nor serotonin. Northern blot analysis demonstrated that the addition of methamphetamine into the cultured medium increased the mRNA level for 14.3.3 eta chain in U-251 cells, but did not increase that of GFAP.