A study has been made of the effect of malachite green on potato viruses X and Y using Dakota Red and Aucklander Short Top potato shoot apices in tissue culture. No plants have been freed from either virus X or Y and there has been no statistically significant effect of the dye on virus X concentration as indicated by local lesion counts on Gomphrena globosa L. Malachite green either sprayed on the leaf surfaces or watered on the soil had no effect on the systemic spread of a ringspot isolate of virus X inoculated to Nicotiana glutinosa L.