When [14C]sucrose was applied to 1 of the primary leaves of bean plants and the small application site subsequently removed, far higher amounts of alcohol-soluble 14C were detected in the leaves of plants under water stress than in controls. The effect could not be accounted for by translocation out of the leaf, nor by synthesis of sucrose into non-alcohol-soluble compounds, nor by respiration. Increased movement of 14C out of the supply area in stressed leaves appeared to be responsible, and the mechanism of [14C]sucrose transport within the leaf was therefore investigated. Subdivision of leaves into sections at brief intervals after 14C application showed that movement of sugar from the treated area was not random, but was directed towards the midvein. This pattern was independent of moisture tension. Radioautographs supported this conclusion, indicating that to both stressed and control leaves labelled sugar was not disposed through the mesophyll but passed from the application site down a sidevein into the midvein. The effect of stress on the movement of THO [tritiated water] in the leaf was the opposite of that on [14C] sucrose, i.e. far less THO was recovered from stressed leaves after removal of the supply area. Accelerated translocation of THO out of the leaf did not account for this result. Nor did exchange with the atmosphere, since the transpiration rate of the control was at least 7 times that of the stressed plants. The gradient in specific activity of THO across the leaf was considerably steeper for control than for stressed leaves. A steam girdle round the stem drastically reduced 14C movement in the leaf in both stressed and control plant. THO movement did not appear to be affected by the girdle. On the basis of the above results it was concluded that movement of applied sugar in the leaf, even over short distances from the application site, was not by capillary flow but involved phloem transport; and that one or more phases of this transport were stimulated by water stress.