Abstract
1. A method is described for the isolation of single-stranded-RNA coliphages. Two of the six RNA coliphages investigated were new strains. 2. The base ratios of six RNA coliphages were determined by labelling the host bacterium with [(32)P]-phosphate, purification of the radioactive coliphages and separation of 2',3'-ribonucleotides liberated by alkaline hydrolysis of the coliphage RNA. 3. All six of the coliphages were morphologically similar, contained single-stranded RNA, and had sedimentation coefficient 80+/-5s. 4. The six RNA coliphages fell into two distinct groups, both serologically and in terms of their RNA base ratios.