The cell water balance of maize (Zea mays L., cv LG 11) andpearl millet (Pennisetum americanum L., cv MH 179) duringosmotic stress was studied non-invasively using 1H nuclearmagnetic resonance (NMR) microscopy. Single NMR parameter imagesof (i) the water content (ii) the transverse relaxation time (T2)and (iii) the apparent diffusion coefficient (Dapp)were used to follow the water status of the stem apical region duringosmotic stress. During stress there are hardly any changes in watercontent or T2 of the stem region of maize. Incontrast, the apical tissue of pearl millet showed a ∼ 30% decreaseof T2 within 48 h of stress, whereasthe water content and Dapp did not change. Thesechanges can be explained by an increase of the membrane permeabilityfor water. This conclusion is supported by results from scanningelectron microscopy, relaxation measurements of sugar solutionsand numerical simulations of the relaxation and (apparent) diffusionbehaviour of water in a plant cell.