Background and Aims The application of deficit irrigation to grapevines modifies the hormonal status of berries, but little information about the influence of berry hormones on phenological sensitivity to water deficit is available. Therefore, the aim of this research was to assess the involvement of berry hormonal status in fruit composition in response to regulated deficit irrigation applied during different phenological stages in two grapevine cultivars. Methods and Results The study was carried out on fruiting cuttings of two cultivars of Vitis viniferaL., Tempranillo and Graciano. Treatments were: (i) early water deficit from fruitset to onset of veraison (early deficit); (ii) late water deficit from onset of veraison to harvest (late deficit); and (iii) plants regularly irrigated (Control). Both early water deficit and late water-deficit strategies modified evolution of indole-3-acetic acid, abscisic acid, salicylic acid and jasmonic acid, which was related to changes in berry size, increases in phenolic substances and accumulation of amines. Conclusions Differential sensitivity of Tempranillo and Graciano grapevines to seasonal water stress was mediated, at least in part, by alterations in hormonal status of berries at the time of water stress imposition. Significance of Study This study relates interspecific differences in the sensitivity of seasonal water-deficit irrigation to changes in the endogenous hormonal status of berries.