An interrelation of Cd-contents with hepato- and nephrotoxicities, and a mechanism for Cd-exclusion from kidneys were investigated in rats that received a single intravenous injection of either CdCl2 or Cd-saturated metallothionein II (Cd-MT-II) with doses of 0.1 and 0.3 mg Cd/kg body weight (b.w.). Between the livers and kidneys, higher uptake of Cd was observed in the liver in terms of CdCl2, and in the kidney in terms of Cd-MT-II. The CdCl2 at the two doses hardly showed any histopathological alterations in the livers and kidneys. The 0.1 mg Cd/kg b.w. of Cd-MT-II showed a slight injury in the kidneys, while hardly in the livers. At Day 1 of the 0.3 mg Cd/kg b.w. of Cd-MT-II, the renal Cd-contents reached the maximal value of 8.22 +/- 0.36 microgram/g wet tissue, and degeneration including necrosis and defluxion of proximal tubular cells were most highly observed. At Day 5 of the 0.3 mg Cd/kg b.w., the renal Cd-contents were lowered to 2.40 +/- 0.24 micrograms/g wet tissue, and fibrosis and regeneration of the proximal tubular cells were remarkably found. These findings strongly suggested that, in the case of administration of Cd-MT-II, the Cd taken into the kidneys was eliminated from there mainly by cellular death of the proximal tubulus and by their resultant defluxion.