Shoot and root mass of tobacco plants treated with only 0.05 μM boron was decreased by 25 and 50 %, respectively, when compared to plants sufficiently supplied with B (2 and 5 μM). Leaf B content of 0.05 μM B-treated plants decreased (about 80 -90 %) when compared to 2 μM B treated plants; this drop of B content were not as marked (about 25 -45 %) in roots. Leaf and root nitrate contents in B-deficient plants were 45 -60 % and 35 -45 % lower, respectively, than those from 2 and 5 μM B treated plants. It is suggested that B deficiency might decrease nitrate uptake rather than nitrate reductase activity in tobacco plants.Additional key words: boron deficiency, hydroponic culture, Nicotiana tabacum, nitrate assimilation.