A metallothionein-like protein has been identified recently in the rat brain which resembles in some but not all aspects a hepatic metallothionein. The synthesis of this protein is stimulated following the administration of zinc and copper but not cadmium. The zinc-stimulated protein incorporates 35S cysteine 24-fold higher than the native, unstimulated protein; is blocked by actinomycin D; produces two isoforms by ion exchange chromatography on DEAE Sephadex A 25 columns; and, by high performance liquid chromatography, depicts a similar but not identical profile to zinc-stimulated hepatic metallothionein. Preliminary studies have shown that the metallothionein-like protein isoform I possesses a Mr of 6200 and consists of 60 residues with 12 cysteine and no histidine, arginine, leucine, tyrosine, or phenylalanine. Since the synthesis of this protein is reduced in the brains of zinc-deficient rats, it is postulated that the free pool of zinc may serve as one of the factors that regulates the synthesis of this protein.