Summary Isolated leaves of ecologically different plants (mesophytes: Pisum sativum L., Helianthus annuus L., Vicia faba L.; hygrophytes: Tradescantia × andersoniana Ludw . et Rohw. , Menyanthes trifoliata L. and Mentha aquatica L.) were wilted for a short time, so that the fresh weight was reduced to 80–60 % of that of the original. Subsequently they were transferred to water for recovery. During the stress period and during the time of recovery, the stomatal pore size and the abscisic acid (ABA) content of the leaves were measured. A delay in the opening reaction of the stomata relative to the recovery of leaf turgor was observed with the mesophytes. The duration of this after-effect of stress on stomatal opening was directly correlated with the ABA level. The ABA level increased two-to five-fold during the stress period and decreased after the stressed leaves had been transferred to water. The application of (±)-ABA to stressed leaves for a duration of one hour after the transfer to water prolonged the duration of stomatal closure, the prolongation being dependent on the concentration applied. The applied ABA increased the ABA level of the leaf and this level decreased subsequently in the same manner as did the natural ABA level. In the hygrophytes investigated, the stomatal opening was not delayed relative to recovery of leaf turgor, and the ABA level did not increase in response to water stress but remained constant ( Menyanthes ) or decreased ( Tradescantia, Mentha ). It is concluded that the after-effect of wilting on stomatal opening is caused primarily by the increased level of ABA. The possible importance of the delay of stomatal opening in the stress physiology of mesophytic and hygrophytic plants is discussed.