Tissue pieces from recently harvested potato tubers infected with. the leaf roll virus when grafted on adequate test plants induce symptoms within 30-45 days. From several species used in comparative tests, Datura stramoniumproved best. Scion tissues from tubers infected with primary or secondary leaf roll gave the same transmission results. Tissues from the vascular apical end of the tubers gave a slightly higher take (67.8%) than comparable tissues from stolon end (56.3%), but transmission was always positive when tissue union took place. Scion tissues taken from the non-vascular inner part of the tubers gave a low transmission (8.0%) even when the scion remained alive for a long time and apparently took (60.0%). The test is considered as of practical value for the determination of late spread of potato leaf roll virus in seed potato fields and can be carried out with tuber samples collected before harvest.