European corn borer (ECB) (Ostrinia nubilalis Hbn.) is currently the most dangerous maize pest in Poland. During last five years the pest was recorded in 14 Polish voivodeships, covering over half of the country's area. The greatest harmful activity of the caterpillars was observed in warm southern regions of Poland. Field experiments carried out in southern Poland in the 2006-2007 growing seasons demonstrated that the average plant damage of non-Bt hybrids by O. nubilalis caterpillars varied between 40.0% and 44.0% in 5 locations and two seasons. Under the same pest pressure a high level of resistance of genetically modified (GM) Bt maize (MON 810) cultivars, expressing Cry1Ab toxic protein to infestation by ECB was noted. The average plant infestation of transgenic hybrids was equal to 0.5-0.7% in the same locations. Only some slight symptoms of injuries, such as small number of holes in stalks and gnawing of cobs was observed. Moreover, the tested transgenic hybrids demonstrated a high suitability for climate and soil conditions in Poland, providing early crops of high yield.