In a lysimeter study with undisturbed soil monoliths the environmental behaviour of the 14C/15N-labeled slow release fertilizer acetylene diurea (ADH) applied together with urea as a readily available N-source (3:1) was investigated. As a comparison a lysimeter was applied only with 15N-labeled urea. All the lysimeters contained undisturbed soil monoliths of a gleyic cambisol. Their surface area was 1 mē and the monolith was 1.1 m deep. A control plot surrounding the lysimeters ensured growth conditions for the experimental plants similar to a field crop. During the three-year research period (2000-2003) plants, soil and percolate were analyzed for their 14C-content and 15N-content. The annual rainfall of 799-828 mm was supplemented by additional spray irrigation to ensure a minimum of 850 mm per year. The annual discharge was about 44-46% of the total precipitation. The total leachate quantity was 1114.3 L as a mean for two ADH lysimeters and 1073 L for urea lysimeter over three years. These leachates contained 0.19% of the applied radioactivity. The 15N-discharged was 6-8 % of applied 15N very similar in all lysimeters over the three years. The crops oat, winter barley and winter wheat took up 0.17 and 0.20% of the applied 14C-activty and between 41.19% and 45.01% of applied 15N in the ADH lysimeters and 33.11% for the urea lysimeter. The most significant reduction of applied radioactivity (AR) in the soil was observed 33 and 36 days after 14C[ADH] application. At the end of the experiment the 14C-activity in the soil was further reduced to an average 5.6% AR, predominantly found in the upper 30 cm (5,3% AR). No 14C-activity was found above the detection limit below 70 cm.