The hepatic metallothionein was isolated and partially purified from rats treated previously with stable Cl2Cd and Cl2Cd109. The livers were subjected to the extraction of proteins of low relative molecular weight by heat, ammonium sulphate, Sephadex G-25 and Sephadex G-75. The partially purified extracts were subjected to the pharmacological activity test on isolated mouse vas deferens. A specific effect on the norepinephrine synapsis was obtained through an increment of the answer to the electric stimulus. The mechanism of action could be explained by the increase of the calcium permeability through the membrane or by the increment of the norepinephrine presynaptic release.