SummaryCross‐protection experiments were performed inChenopodium quinoausing arabis mosaic virus (ArMV) and grapevine fanleaf virus (GFLV) isolates.Two factors were specially studied, namely the time interval and the distance between the two inoculations, respectively, with the hypovirulent isolate and with the hyper virulent challenge isolale.ArMV‐S clearly protectedC. quinoafrom a super infection with GFLV‐F13 as shown by a diminution, or even suppression, of the synthesis of the coat protein and the nucleic acids of the GFLV‐F13 isolate. In the homologous interaction between GFLV isolates (GH and F13), protection was also observed. In the interaction between GFLV‐GH and ArMV‐862, by contrast, symptoms were typical of the hyper virulent ArMV‐862 and the amount of coat protein of ArMV