Four naturally occurring strains of tobacco mosaic virus, U2, Dahlemense, CV4, and the bean form of tobacco mosaic virus, were tested for the existence of long T1 RNAase oligonucleotides analogous to the oligonucleotide omega found in the common or U1 strain of tobacco mosaic virus and which makes up the 5' non-coding region of the RNA molecule. U2 and Dahlemense RNA were each found to contain this type of long T1 RNAase oligonucleotide with chain lengths of 54 and 74--77 residues, respectively. The sequence of the two oligonucleotides was determined mostly by using 5'-32P-labelled material in vitro and rapid polyacrylamide gel sequencing techniques.