Leaf roll infection on the interplanted indicator plants, jimson weed, tomato, and a non-identified Physalis species is correlated to spread of the disease in the seed potato field. Result from twelve tests carried out at several localities gave the following infection averages: jimson weed, 49.6%; Physalissp., 34.0%; tomato plants, 28.5%. Potato plants showed an average of 0.9% primary leaf roll, but tuber tests indicated that field spread had been 23.6%. Potato virus Y infected 45.1% of the tobacco plants, 37.3% of Physalissp., and 18.1% of the tomato plants. Potato plants were not infected with this virus because the Ycomplex present was the one that infects tomato and pepper plants and very seldom potato plants in the field. The viruses of tomato curly top and Brazilian tobacco streak infected jimson weed at the average rates of 16.1% and 2.7%, respectively. Tomato plants showed an average of 4.1% of curly top, but no infection with the Brazilian tobacco streak virus. Potato plants were not affected by these viruses. Tomato spotted wilt virus infected several of the indicator species and also the potato plants, but there was no perpetuation of the virus through the tubers. Interplanting indicator plants in the certified seed potato fields is suggested as a means to estimate the extent of leaf roll spread in the crop.