Extracting of a root system from the soil without losses is the main difficulty in investigations of the potato root system. In the years 1992-1998 at The Potato Research Institute, Jadwisin (Poland) an original method for potato root system investigation was developed. A special pot (40 cm in diameter, 100 cm high) made of zinc coated steel sheet 0,8 mm was constructed. This device may be opened lengthwise to obtain the whole intact root system of potato plant. Soil profile in the pot is formed in 10 horizontal layers separated by circles made of plastic mesh which enable distinguishing of roots related to certain soil horizons. The method described makes possible (in a relatively easy way) taking measurements of weight and length of roots in every 10-cm layer of soil up to depth of l meter, so as to assess: the weight of fresh and/or dry matter and length of the whole potato plant root system and its distribution in the soil profile. This method might be useful also for investigation of root systems of another species.