The effects of different irrigation techniques on leaf xylem ABA concentration ([X-ABA]_leaf) were compared in tomato (Lycopersicon esculentum Mill.). During partial rootzone drying (PRD), water was distributed unevenly to the root system such that part was irrigated while the remainder was allowed to dry the soil. During conventional deficit irrigation (DI), plants received the same volume of water as PRD plants, but water was distributed evenly to the entire root system. When the plant root system was allowed to explore two separate soil compartments, DI plants had a higher [X-ABA]_leaf than PRD plants with moderate soil drying, but PRD plants had a higher [X-ABA]_leaf than DI plants as the soil dried further. The difference in [X-ABA]_leaf between the two sets of plants was not because of differences in either whole pot soil water content (θ_pot) or leaf water potential (Ψ_leaf). To investigate the contribution of different parts of the root system to [X-ABA]_leaf, individual shoots were grafted onto the root systems of two plants grown in two separate pots, so that the graft union had the appearance of an inverted ‘Y’. After sap collection from detached leaves, removal of the shoot below the graft union allowed sap collection from each root system. Again, DI plants had a higher [X-ABA]_leaf than PRD plants when the soil was relatively wet, but the opposite occurred as the soil dried. Root xylem ABA concentration ([X-ABA]_root) increased exponentially as soil water content (θ) declined. In DI plants, [X-ABA]_root from either pot (or the arithmetic mean of [X-ABA]_root) accounted for a similar amount of the variation in [X-ABA]_leaf. In PRD plants, [X-ABA]_root from the watered side underestimated [X-ABA]_leaf, whereas [X-ABA]_root from the dry side overestimated [X-ABA]_leaf. The arithmetic mean of [X-ABA]_root best explained the variation in [X-ABA]_leaf, implying continued sap flow from the dry part of the root system (J_dry) at soil water potentials (Ψ_soil) at which J_dry had ceased in previous studies of PRD plants (Yao et al. 2001). Evaluating the relationship between J_dry and Ψ_soil may assist in maintaining export of ABA (and other growth regulators) from the drying part of the root system, to achieve desirable horticultural outcomes during PRD.