Translation of alfalfa mosaic virus (AMV) RNAs in the mRNA-dependent rabbit reticulocyte cell-free system was examined using different RNA concentrations. The pattern of products synthesized under the direction of AMV RNA 2, 3 and 4 was not or almost not influenced by their concentration. However, depending on the RNA 1 concentration either a very large protein of Mr 115,000 or a mixture of two smaller proteins, Mr 58,000 and 62,000 respectively, was formed. These three proteins represent overlapping peptide chains with identical N-termini. Addition of the cap analogue 7-methylguanosine 5'-monophosphate (m7GMP) or AMV RNA 3 stimulated the production of the 115,000-Mr protein at the expense of the 58,000-Mr and 62,000-Mr proteins. Both m7GMP and RNA 3 probably reduce the active concentration of RNA 1 by competing for (a) cellular component(s) necessary for translation. These experimental results suggest that the rate of translation beyond the C termini of the 58,000-Mr and 62,000-Mr proteins is reduced or completely inhibited owing to the limited availability of the succeeding tRNA(s).