Recently, we have shown that nitrate concentration in cubital venous blood decreases during short, exhausting cycle exercise. In this investigation we evaluated the nitrate concentration in blood draining the working muscles during exhaustive forearm exercise. 9 male subjects performed 2 maximal exercise bouts separated by a break of 60 s followed by 30 min of recovery. Blood was taken from an arterialized hand vein and from a cubital vein of the working muscles. In plasma, nitrate and nitrite were determined by GC-MS. Lactate, pH and blood gases were analysed by conventional methods. Forearm blood flow was determined by venous occlusion plethysmography. Release or uptake was calculated according to the Fick principle. Lactate in cubital venous plasma increased to 13.5 ± 3.2 mmol/l and PCO2 to 102.3 ± 9.5 mmHg. HbO2 decreased to 26.5± 5.7 % and pH fell to 7.115 ± 0.034. Nitrate concentration in arterialized blood remained almost constant during exercise and the recovery period. Venous nitrate concentration decreased slightly (p<0.001) during the early recovery period. However after correcting the data for water shifts due to osmosis the decrease of nitrate concentration was enhanced. The lowest value was found at the end of exercise (p<0.001). Nitrate concentration remained lower than the resting concentration until the 8^th min after exercise (p<0.003). The loss of nitrate from the plasma was maximal at the end of exercise (63.8 ± 74.8 mmol/ min/l tissue; p<0.001). Such changes have not been seen for nitrite. The data show that nitrate may serve as a readily accessible nitrogen store for NO production during exhaustive exercise.