In order to investigate the role of metallothionein in acute cadmium (Cd) toxicity, the following results were obtained by administrating cycloheximide to mice. 1) The concentration of metallothionein in the liver of mice to which Cd and cycloheximide were administered decreased more than that given only Cd. 2) Metallothionein did not take part in the incorporation of Cd into the liver. 3) The rate of death in the mice to which Cd and cycloheximide were administered increased. 4) The concentration of metallothionein in the liver of mice given Cd and cycloheximide decreased with an increase in the amount of Cd administered. 5) After metallothionein was induced by Cd, the concentration of metallothionein in the liver of the group given cycloheximide was higher than that of the group to which no cycloheximide was administered.