RNA was isolated from HBsAg particles obtained by the method of preparatory immunoprecipitation with anti-HBs antibodies. RNA electrophoresis in polyacrylamide gel showed presence of one fraction with molecular weight about 28 000. The index of RNA sedimentation determined by the method of ultracentrifugation was about 4 S. RNA from HBsAg had no informative features of nucleic acids (m RNA) such as presence of methyl group 5' of the end sequence m7 GpppN ("cap"), translatory activity. It had also no features of tRNA since it was not aminoacylated in the presence of aminoacylo-tRNA synthetases.