Zinc participates extensively in the metabolism of carbohydrates, lipids, proteins, and nucleic acids and therefore is essential for the growth and development of all organs, including the brain. The concentrations of zinc in various regions of developing rat brain are nonuniform, and either remain the same or decline dramatically. Studies involving gel permeation chromatography on Sephadex G-75 have shown that unlike the hepatic metallothionein, the concentration of a metallothionein-like protein increases postnatally in the brain from 0.2 μg in 1 d after birth to 3.60 μg zinc/mg protein in 50 d after birth. Furthermore, high-performance liquid chromatographic studies have shown that the adult rat brain contains three small-molecular-weight zinc-binding proteins, one of which is stimulated following intracerebroventricular administration of zinc, producing metallothionein-like isoforms I and II, with retention times of 17.32 and 18.64 min, respectively. All three zinc-binding proteins are absent in the brains of newborn rats. It is proposed that the developmental alteration in the concentration of brain metallothionein-like protein may be related to zinc-mediated functions associated with the development and the maturation of brain.