The effect of the rootstock on scion water relations was evaluated in container-grown Prunus plants. The leaf water potential (ψw), stem sap flow (SF), and canopy transpiration (E) of peach grafted onto three peach x almond hybrid rootstocks ('GF 677', 'I.S.5/23' and 'I.S.5/29') were compared with those of the rootstock plants under irrigated and unirrigated conditions. The three rootstocks were different in vigour and induced productivity. The leaf ψw of cultivar/rootstock combinations were higher than those of the rootstock only but SF and E were lower in the cultivar/rootstock combinations than in the rootstock only for all three rootstocks. The highest E was measured in the least vigorous rootstock ('I.S.5/23') regardless of the presence of the scion cultivar. Differences in ψw, SF, and E were mainly attributable to the characteristics of the root system and the canopy/root relationships established after grafting.