A comparison of 50 pairs of field healthy and leaf roll infected potato plants of nine varieties indicated that the total yield reduction was on the average 60.7 per cent. Yield reduction of the two largest and most marketable potato sizes ("especial" and "primeira") reached 75.6 per cent. Aquila and Gunda had the highest yield losses (73.4 and 72.0 per cent); Delta A and Patrones had the lowest (47.6 and 44.6 per cent). Reduction in the yield of the larger tuber sizes was generally greater than total losses.