Studies on the dynamics of concentrations and discharge of nitrogen load through draining systems were carried out in Olsztyn Lake District (Pojezierze Olsztyńskie) from1994 to 2007. For the tests, three basins were selected: an agricultural basin drained with a drainage system, an agricultural and forested basin drained with a network of ditches and drains, and an agriculrual basin with a large forest cover (ca 30%), drained with ditches. The discharge of water through the draining facilities was measured every two weeks, and once a month, N-NO3, N-NO2, N-NH4 as well as Kjeldahl nitrogen were determined. It has been demonstrated that the volume of discharged water carried away through draining systems depends primarily on the amount and distribution of atmospheric precipitation, epsecially during the winter half-year. The dynamics of concentrations and loads of nitrogen in water discharged via draining systems varied with time and depended not only on the amount and distribution of precipitation over a year and in the multi-year period, but also on the type of land use in a given basin and a draining system. It was also foundout that intensive rainfall in summer only slightly increased the discharge of water from the basinm drained with the drainage system. The load of total nitrogen flowing away through the draining systems from agricultural basins was closely connected with the amountof discharged water and water levels of mineral nitrogen compounds, especially N-NO3. The highest nitrogen loss from drained areas appeared in spring, which was associated with the seasonal character of water outflow, culmunating in March-April. The highest concentration of total nitrogen (16.69 mg dm–3) was determined in water discharged through the network of ditches and drains, but due to a more intensive dewatering of soils, a higher total nitrogen load (on average 33% more) was discharged through drains. Per 1 ha of an agricultural basin, the annual outflow of total nitrogen was up to 13.13 kg, including 12.04 kg of mineral nitrogen.