Guanidine does not inhibit the translation of viral RNA into virus specific proteins but it seems to prevent the generation of functional viral polymerase from precursor material. In the presence of guanidine, "inhibitory protein (s) " responsible for the shut-off of cellular protein synthesis are still produced provided that the multiplicities of infection are high. The incoming (parental) viral RNA appears to be functional as messenger for only a limited number of translational cycles.