Barley straw with a 13 or 35% moisture content was treated on a laboratory scale with 5.25 g of urea/100 g DM at 20 or 40°C for 5 or 10 weeks with or without urease. The higher moisture content resulted in a 14 percentage units increase in straw degradability, whereas the lower moisture level gave 7 units of improvement in relation to untreated straw. Urease addition, elevation of temperature or prolonged treatment time were less effective. Significant amounts of added urea avoided decomposition during treatment. Barley straw with an approximately 25% moisture content was treated under field conditions with a 25% ammonia solution (2.6 kg NH₃/100 kg) or with a 40% urea solution (5.0 kg urea/100 kg straw DM) for 6 weeks with a straw temperature of about 15°C. Twenty one-year-old wethers of about 46 kg body weight, in 4 groups of five, were fed untreated barley straw to appetite (540 g/d), ammoniated straw (550 g/d), ammoniated straw to appetite (790 g/d) or urea-treated straw to appetite (550 g/d), respectively, for one month. Ammonia treatment decreased the structural carbohydrate fractions content but significantly increased the nitrogen content, straw intake and nutrient digestibility, whereas urea treatment gave only slight straw upgrading. Degradability in situ of ammoniated straw DM was about 9.2, but urea-treated only 1.5 percentage units higher than untreated straw. Animals fed ammoniated straw to appetite gained about 60 g/day during the experimental period whereas animals fed untreated and urea-treated straw, offered to appetite, or rationed ammoniated straw lost about 100 g/day demonstrating that only ammoniated straw fed to appetite covered the maintenance level of nutrient requirement. Urea was poorly hydrolyzed to ammonia during treatment at dominating in this region climatic conditions (15°C) which was demonstrated in the high urea content in urea-treated straw and what could be the reason for inconsiderable straw upgrading with the applied method.