Studies were carried out on the effect of inoculation with Azospirillum brasilense on development and yielding of winter wheat and oat. Plants were grown in the field conditions. In the experiments conducted in randomized block design, three factors were applied: inoculation with an active strain of Azospirillum brasilense, two levels of nitrogen fertilizer and seed treatment with fungicidal seed dressing. It was found, that inoculation of cereals with active strain of Azospirillum brasilense may be a factor increasing their vigour and yielding. Under climatic and soil conditions of Wielkopolska region and despite the fact, that no dinitrogen fixation was observed, cereal inoculation with Azospirillum brasilense contributed to the yield increase up to 27% in wheat and to 6% in oat.