All ten reovirus genome RNA segments were radiolabeled at their 3'-termini by incubation with RNA ligase and 32pCp. The extent of radiolabeling was similar for each of the double-stranded RNAs in the genome segment mixture. Radioactivity was equally distributed between the separated plus and minus strands indicating that the 5'-cap in plus strands did not block 3'-end-labeling of minus strands. The 3'-termini of the four S and three M segments included the common sequences: ...U-A-G-C in minus strands and ...U-C-A-U-C in plus strands. By comparing the minus strand 3'-sequences with 5'-sequences of reovirus mRNAs, small-size genome segments S2, S3 and S4 were correlated with the previously sequenced initiation fragments s46, s45 and s54 derived from small class mRNAs. Medium-size genome segments M1, M2 and M3 similarly were correlated with fragments m30, m52 and m44, respectively. The N-terminal amino acid sequences deduced from the mRNA nucleotide sequences can now be assigned to the nascent chains of particular reovirus proteins.