S U M M A R YCrude cell-free amino acid-incorporating systems derived from a variety of enterobacterial species are not uniform in their ability to translate RNA of the coliphages Qp or MS 2 . Escherichia coli, Shigella alkalescens and to a lesser extent Citrobacter freundii translate effectively under standard conditions, but Salmonella typhimurium, S. pomona and Proteus morganii do not. Ineffective species do not generally inactivate phage RNA faster than effective ones, and they are as effective as E. coli in their general capacity for mRNA translation. This was judged in representative species by the incorporation of phenylalanine and leucine labels as directed by polyuridylate or mRNA of phage-infected S. typhirnurium, and from the relative incorporation of methionine label into the normal initiating N-formylmethionine residues of polypeptides. The ribosomal rather than the soluble components appear responsible for ineffectiveness in translation.