Vesicular stomatitis virus (VSV) and defective interfering (DI) particle RNAs were labeled at their 3' ends by using RNA ligase and cytidine 3',5'-bis[32P]phosphate. The RNAs were subjected to partial digestion with alkali and analyzed by oligonucleotide fingerprinting in two dimensions. VSV and DI particle RNAs have complete sequence homology for the first eight bases from the 3' end. The following four positions contain three mismatched nucleotides in which guanosine residues in one strand are replaced by uridine residues in the other. There is again complete homology for the next five bases (positions 13-17). The locations of purine residues within the sequence were confirmed by partial digestion with RNase T1 and RNase U2 and separation by size on 20% acrylamide gels. The latter method also indicated that sequences of VSV and DI particle RNAs diverge beyond the 18th nucleotide from the 3' termini.