Abstract The translation of poliovirus RNA and vesicular stomatitis virus (VSV) mRNAs was studied in reticulocyte lysates supplemented with uninfected HeLa cell or polio-infected HeLa cell ribosomal salt wash as a source of initiation factors. Ribosomal salt wash from uninfected HeLa cells supported translation of both RNAs. Similar preparations from polio-infected HeLa cells stimulated translation of polio RNA; however, the translation of VSV mRNAs was completely restricted. Lysates programmed simultaneously with polio RNA and VSV mRNA translated both RNAs, although VSV translation was predominant. Addition of polio-infected cell ribosomal salt wash resulted in translation of polio RNA exclusively. The infected cell salt wash did not prevent formation of 40 S·Met-tRNA f Met complexes, but did prevent binding of labeled VSV mRNA to 40 S initiation complexes. The ability to restrict VSV mRNA translation resided in the 40% ammonium sulfate fractional precipitate prepared from infected cell salt wash. Similar fractionation of ribosomal salt wash mixed with labeled poliovirus double-stranded RNA indicated that this component was also found in the 40% ammonium sulfate fraction. The effects on translation of double-stranded RNA and the restrictive activity of infected cell salt wash were compared: mRNA specificity, kinetics of inhibition, nuclease sensitivity, and relief of inhibition by excess double-stranded RNA differed. From these comparisons, the possibility that double-stranded RNA caused the restriction of VSV mRNA translation was excluded.