The effects of Daehengqi decoction (DCQ) and rhubarb (Rb) on the spontaneous cellular electrical activities of guinea pig taenia coU have been studied by intracellular microelectrode technique. DCQ and Rb both improve the depolarization of cell membrane, speed up the burst of slow wave and spike potentials (when the drug concentration was 1%, P>0.05, 10% or 20%, P<0.03), which were dose de pendent. At the same concentration the effects of Rb were more significant than those of DCQ. These results suggest DCQ and Rb directly enhance the cellular electrical excitability so as to strengthen the con traction of the colon, is one of the mechanisms of the purgative action of these drugs at the cellular level. The ionic basis of the effects might be that DCQ and Rb reduce the K+ conductance of the cell membranes in a resting state.