AbstractL–A–E double‐stranded RNA (dsRNA), when introduced into cells carrying L–A–H and M2dsRNAs, does not eliminate the L–A–H dsRNA, but (i) L–A–E does lower the copy number of L–A–H dramatically and (ii) L–A–E eliminates M2dsRNA from the cell. That these two effects of L–A–E are related is shown by the fact that mutants of a strain carrying L–A–H and M2selected for their resistance to exclusion of M2by L–A–E [effect (ii)] have an altered L–A–H whose copy number is not lowered by L–A–E [effect (i)]. Although the L–A in K1strains (L–A–HN in all cases examined) differs significantly both genetically and physically from the L–A in the K2strain studied (L–A–H), the L–A–HN from the K1strains can maintain M