In rabbit reticulocyte lysates the RNAs of encephalomyocarditis (EMC) virus, mengovirus, and Mous-Elberfeld (ME) virus directed the synthesis of similar sets of products. Moreover, the viral protease synthesized from any one of the three viral RNAs could cause cleavage of the viral capsid precursor proteins synthesized from any of the three RNAs. However, the three RNAs differed in their dependence on tRNA supplementation (to the lysates) for effective translation. In the absence of tRNA supplementation, synthesis of 5'-derived proteins of EMC viral RNA proceeded normally, but little synthesis of the proteins coded by the remaining portion of the viral genome occurred. In the case of mengoviral RNA, omission of tRNA supplementation caused mostly a generalized reduction of the synthesis of all viral proteins. In contrast, synthesis of ME viral proteins stopped almost completely in the absence of tRNA supplementation.