Tetrathiomolybdate (TTM) was injected at a dose of 10 mg/kg bw daily for eight consecutive days into Long-Evans Cinnamon (LEC) rats, which inherently abnormally deposit Cu (260 micrograms/g) in the liver. The hepatic Cu (100 micrograms/g) and metallothionein (MT) bound Cu (from 2,600 to 540 micrograms/g protein) concentrations were decreased greatly by the injection. On the other hand, the renal Cu concentration increased significantly, but the brain Cu concentration only very slightly. The reduction of the hepatic Cu concentration was accompanied by reductions of Zn and Fe concentrations in the liver, kidney and brain. The TTM compound slightly stimulated excretion (about 3-fold) of Cu into the bile, but greatly (about 40-fold) into the blood. In rats not treated with TTM, most biliary (100%) and serum (78%) Cu was recovered in the trichloroacetic acid (TCA) soluble fraction. On the other hand, in rats treated with TTM, bile and serum Cu were recovered overwhelmingly in the TCA insoluble fraction, probably in the form of a Cu-TTM-albumin complex. Our results suggest that although there is an inherent failure in the intrinsic secretory process of Cu from the liver in LEC rats, the TTM compound can remove Cu from Cu-MT, resulting in a decrease of hepatic Cu.