Changes in the numbers of Azospirillum bacteria were studied in soil under winter wheat, oat and maize crops. The cereal seeds were treated with fungicides and inoculated with Azospirillum brasilense actively fixing dinitrogen. Plants were grown without nitrogen fertiliser and with nitrogen application in the amount of 60 and 120 kg N ha(-1) for wheat, 50 and 100 kg N ha(-1) for oats and 100 and 200 kg N ha(-1) for maize. The population number of bacteria was estimated at different developmental stages of plants. inoculation of cereals with Azospirillum brasilense bacteria contributed to the increase of their numbers in soil. No significant influence of fungicidal seed dressings on the numbers of Azospirillum bacteria has been noted. The application of mineral nitrogen to the crops was favourable to multiplication of Azospirillum bacteria under plants.