Raspberry bushy dwarf virus (RBDV) was transmitted to raspberry seed both through the pollen and through the ovule and it infected plants pollinated with infected pollen. It did not infect plants prevented from flowering, and transmission through pollen seems to be the only method of spread in the field. In the proximity of infectors, most plants became infected during the first 2 or 3 flowering seasons. Plants containing RBDV showed no obvious symptoms, but healthy or infected flowers pollinated with infected pollen produced 'crumbly' fruit, containing a high proportion of aborted drupelets. RBDV was difficult to eliminate from infected raspberry by heat therapy. Raspberry cvs that fail to become infected naturally were also immune to infection by grafting. The use of immune cvs so far offers the only method of control.