SUMMARYTurkey and chicken rotaviruses were successfully adapted to replicate in a rhesus monkey embryo kidney (MA104) cell line. Trypsin treatment of virus and cells was essential for serial passage of the viruses. Polyacrylamide gel electrophoresis separated the viral RNA into 11 segments with clear resolution of segments 10 and I 1. Segment 5 migrated with size class I, and this characteristic appeared to be a unique feature of the avian rotavirus genome. The ability of the avian rotaviruses to haemagglutinate a variety of erythrocytes was demonstrated. A type-specific antigen was detected by haemagglutination-inhibition assays and a group or subgroup antigen by enzyme immunoassays. Treatment of serum with heparin-MnC12 was shown to be the best method for removing non-specific inhibitors of haemagglutination.