Leaf-elongation rates of Zea mays L. and Phaseolus vulgaris L. were measured in plants grown for 4 d in nutrient solution bubbled with N2 and in soil-grown waterlogged Phaseolus plants. Leaf water potential in both species was lower 3-4h after replacing aeration by N2-bubbling. In Zea, the water potential after 24 h or more was the same in control plants and plants with N2 treatment. In Phaseolus, the water potential of inundated plants and plants with N2 treatment was always lower than those of control plants. The leaf-elongation rate of both species was always lower in plants treated with N2, especially during light periods. In Zea, the elongation rate was lowest in the first 24 h, whilst in Phaseolus it was lowest on the last (fourth) day of treatment. There was no difference between N2 treatment and inundation experiments. It is concluded that during the first hours of treatment the leaf-elongation rate was reduced as a consequence of the lower water potential. Thereafter, however, elongation rates were lower than could be expected on the basis of the plant's water relations.