Preparations of ribosome subunits from the rabbit liver are completely free from the endogenic mRNA admixture and high-active in a system of codon-dependent binding of tRNA. Leucine codons of uridyl-uridyl-adenine (UUA) and uridyl-uridyl-guanine (UUG) are synthesized by the triester method. The correspondence of six leucine isoacceptor tRNA from mammary gland of cows to cytidyl-uridyl-uridine (CUU), UUA and UUG codons is studied. The code response of tRNA is compared with their ability to erroneously translate polyuridylic acid.