The temperature-sensitive mutant of yeast, rna2-, when incubated at the nonpermissive temperature, has a qualitatively distinct distribution of mRNA sequences as compared to wild-type. Quantitative comparison with the wild-type distribution indicates that after 1 hr at the nonpermissive temperature, the concentration of approximately 100-150 abundant sequences is significantly decreased. Control experiments indicate that this effect is not simply a function of the increase in incubation temperature nor a general effect on all mRNAs. Gorenstein and Warner (1976) have shown that the synthesis of ribosomal proteins is preferentially depressed at the non-permissive temperature in rna2-. It is proposed that among these 100-150 sequences are the mRNAs which code for the ribosomal proteins.