Summary.The effect of the herbicidal compound dicamba (2‐methoxy‐3,6‐dichlorobenzoic acid) on the rate of oxygen uptake and on cell membrane permeability of leaf tissues of purple nutsedge (Cyprus rotundusL.) was studied. Dicamba induced noticeable alterations in both the pattern of oxygen consumption and in permeability of the cells following spraying of the foliar parts of the plants. A pronounced decrease in respiratory rate was observed 5 days after treatment with 10−3M dicamba, but the rate of oxygen uptake rose to approximately the level of the control 10 days after application of the herbicide. Permeability of the cell membranes decreased 5 days after treatment of the leaves with 10−2M or 10−3M dicamba. The results indicate that the early disruption of the cell membranes might be related to the mode of action of th