The terminal structure of rotavirus genomic ds RNA and in vitro transcribed mRNA was investigated using S1 nuclease digestion and 3' terminal sequence analysis. S1 nuclease analysis indicated that viral mRNA was not a truncated copy of the genome RNA at its 5' end. The 3' terminal sequence analysis of genomic plus strands and mRNA showed that they were coterminal indicating that in vitro transcribed mRNA is a full length copy of the genomic template. The sequence analysis performed on isolated viral RNA species plus strands revealed a completely conserved 3' terminal octanucleotide 5'-AUGUGACC-3' present in both UK tissue culture adapted bovine rotavirus and a human rotavirus isolate. Sequencing of isolated genomic minus strands again revealed a completely conserved 3' terminal sequence of approximately the same length as that seen for the viral plus strands.