Membrane vesicle traffic to and from the plasma membrane is essential for cellular homeostasis in all eukaryotes. In plants, constitutive traffic to and from the plasma membrane has been implicated in maintaining the population of integral plasma-membrane proteins and its adjustment to a variety of hormonal and environmental stimuli. However, direct evidence for evoked and selective traffic has been lacking. Here, we report that the hormone abscisic acid (ABA), which controls ion transport and transpiration in plants under water stress, triggers the selective endocytosis of the KAT1 K+ channel protein in epidermal and guard cells. Endocytosis of the K+ channel from the plasma membrane initiates in concert with changes in K+ channel activities evoked by ABA and leads to sequestration of the K+ channel within an endosomal membrane pool that recycles back to the plasma membrane over a period of hours. Selective K+ channel endocytosis, sequestration, and recycling demonstrates a tight and dynamic control of the population of K+ channels at the plasma membrane as part of a key plant signaling and response mechanism, and the observations point to a role for channel traffic in adaptive changes in the capacity for osmotic solute flux of stomatal guard cells.