The terminal cis-glycol-group of phenylalanine specific tRNA (tRNA(Phe), I) from yeast was oxidized to the dialdehyde by NaIO(4) (tRNA(Phe)(oxi), II) and subsequently reduced to the diol by NaBH(4) (tRNA(Phe)(oxi-red), III). In charging experiments it could be shown that tRNA(Phe)(oxi-red) is still completely specific for phenylalanine. The Michaelis constant of tRNA(Phe)(oxi-red) remains unchanged when compared with tRNA(Phe), while the maximun velocity of charging upsilon(max) of tRNA(Phe)(oxi-red) is decreased to about one half.