The basic properties of released and cell-associated reovirus are the same. Both contained as their total nucleic acid complement only double-stranded ribonucleic acid (RNA) with an adenine content of 28%. Preparations of purified cell-associated virus, but not released virus, contained adenine-rich RNA which could be separated from the virus with little or no loss of infectivity. These adenine-rich ribonucleic acids were present in the virus preparations either as free RNA or associated with some structures of molecular weight less than 25 x 10(6) daltons. In contrast to our previous report, double-stranded reovirus RNA possessed little or no template activity for the Escherichia coli deoxyribonucleic acid and RNA polymerases.