Abscisic acid was shown to inhibit transport of potassium and chloride from the cut ends of excised barley and maize roots. Transport to the shoot of intact barley seedlings was also inhibited. Total uptake into the excised root of barley did not appear to be affected by abscisic acid. There was an increase in tracer accumulated in the root accompanying the reduction in transport from the cut end. Concentrations of abscisic acid above 10-6M produced the maximum effect.