In the programme of breeding tobacco varieties characterized by the resistance to TSWV it is necessary to control individual generations with regard to their resistance to that virus until homozygous forms are obtained. For this purpose, an accessible and effective inoculate is necessary. That was the aim of the observations carried out in 1984 and the experiments performed in 1985. In 1984 considerable affection of potato plantations near tobacco plantations infected with TSWV was noticed. As a result of these observations in 1985 sound potato plants of Mila variety (maternal material) were inoculated with the virus under greenhouse conditions. After 5-6 days on the infected leaves of potato plants, necrotic brown spots appeared, 3-4 mm in diameter. Similar spots of systemic infection were noticed on the top leaves after 12 days. The infected leaves grew yellow and fell off the stem. Gradually the whole of the potato plants withered. The tubers of the infected potatoes were collected and stored at a temperature of 15-20.degree.C for two months. Then, their soundness was controlled. The tests showed that the majority of the potato tubers contained TSWV. The presence of this virus in the potato tubers was ascertained by the test on petunia and tobacco. In most of the tubers the concentration of TSWV was medium in degree which enabled the infection of young tobacco plants with the juice extracted from potato tubers. Thus, it is possible to obtain a convenient source of TSWV and to infect breeding tobacco material at any season.