A research on the influence of monoculture vs five types of crop rotations on the infection of tobacco by tobacco mosaic virus (TMV) was conducted from 1987 to 1996. The research was carried out on the experimental field of the Tobacco Institute Zagreb in Pitomaca (Northern Croatia) on [luvic semigley, sic ] soil characteristic of the flue-cured tobacco growing region in Croatia. In addition to tobacco monoculture, in the other types of crop rotation, the planting of tobacco came after winter wheat (2-crop rotation, 3-crop rotation, 4-crop rotation, 6-crop rotation) and rape (5-crop rotation). Tobacco was planted every year (monoculture), every second year (winter wheat and tobacco), every third year (maize, winter wheat and tobacco), every fourth year (maize, soybean, winter wheat and tobacco), every fifth year (maize, soybean, winter wheat, rape and tobacco) and every sixth year (red clover, red clover, maize, soybean, winter wheat and tobacco). All crops were repeated four times. Tobacco infection by viruses varied according to year of research. However, even after the third year of research, tobacco in monoculture conditions was significantly more affected by viruses as compared with tobacco grown in crop rotation, when the preceding crop was winter wheat (2-crop rotation, 3-crop rotation, 4-crop rotation and 6-crop rotation) or rape (5-crop rotation). After continued monoculture for ten years, infection by TMV amounted to 27.8% (1996) while for six crop rotation it came to 5.3%. The production of tobacco in monoculture reduced yield from 2.63 t/ha in the first year (1987) to 1.69 t/ha in the tenth year (1996). Tobacco planted in a wider rotation was significantly less infected by TMV, had an increased leaf yield and a tendency to a higher proportion of quality leaf.