Male rats received one injection of a ‘subtoxic’ amount of Cd²⁺ (9.2 µmol/kg body weight) as cadmium chloride and the testes were removed 24 h later. Homogenate fractions of testes that had been freed of ribosomes were tested for their activity in cell-free protein-synthesizing systems using excess exogenous rat liver ribosomes and mRNA. A marked decrease in the incorporation of free [¹⁴C]-phenylalanine into peptide was observed with the testes preparations from the cadmium-treated rats. The results indicated that about half of the effect of cadmium was due to decreased aminoacyl-tRNA synthetase activity and the other half was due to decreased binding of [¹⁴C]-phenylalanyl-tRNA to ribosomes. The results are discussed relative to the contrasting results obtained in kidney and liver preparations.