The rate of damages caused by the field slug Deroceras reticulatum to winter oilseed rape and winter wheat was investigated under field and laboratory conditions. The number and degree of seedling damages were estimated on the basis of the intensity of slug occurrence, which were caught in baited traps. It was found that over a 3-4-week period after sowing, damages caused by D. reticulatum slugs constituted 60% in young oilseed rape and 40% in wheat plants. Under laboratory conditions, one slug damaged almost completely 10 rape seedlings (95%) during 13 days of its feeding. The percentage damage caused by the pest to wheat seedlings was considerably lower (53%), whereas wheat seeds appeared to be severely damaged (83%) after 9 days of the slug feeding.