To study the role of a messenger sugar-phosphate backbone in the ribosomal decoding process, poly(U) and poly(dT) template activity in different eukaryotic systems has been compared. 80S ribosomes from Saccharomyces cerevisiae appeared to be able to translate poly(dT) both in the presence and in the absence of elongation factors, contrary to poly(U). However, ribosomes from higher eukaryotes (wheat germ, rabbit liver) are completely inefficient in poly(dT) translation. Moreover, rabbit liver ribosomes fail to bind effectively phenylalanyl-tRNA in the presence of poly(dT) although the polynucleotide seems to interact with the ribosomal decoding center. It is also of particular interest that hybrid ribosomes formed from the yeast and rabbit liver subunits can translate poly(dT) only when the large ribosomal subunit from yeast is used.