EN
Difficulties in learning Polish as a foreign language by people from the East fall within the scope of interest of glottodidacticians. This paper is an attempt at a practical approach to the subject matter. The presented language material was derived from two texts that were prepared specifi cally as an element of an educational experiment. Its intention was to check the effectiveness of the contrastive method in teaching foreign languages. The paper focuses on three issues related to teaching noun infl ection, which cause problems to speakers of Belarusian and Russian. It presents and discusses language errors being examples of interlingual interference. In accordance with the fi ndings made in the paper, the most common cause of errors is the infl uence of Russian, and Belarusian at times contributes to error fossilisation.