Mechanisms of cell elongation were studied by using soybean (Glycine max [L.] Merr.) embryos subjected to environmental stresses under tissue-culture conditions. Water potential of culture media ranged from -0.02 to -0.80 MPa so that nutrient deficiency and salt stress conditions could be applied to plants grown in the media. According to Lockhart's growth equation, cell expansion is controlled by hydraulic conductance, growth-induced water potential, wall extensibility and effective turgor. All parameters were measured in elongating stems and roots of soybean embryos by using the isopiestic psychrometer and pressure probe. Wall extensibility was significantly larger than hydraulic conductance, and the effective turgor was significantly smaller than the size of the growth-induced water potential. Therefore, we conclude that cell elongation rates were primarily regulated by how much water could be absorbed by elongating cells and the size of the water potential difference between elongating cells and the water source under environmental stresses.