To investigate the actions of Shakuyaku-kanzo-to (SKT), a standardized 1:1 combination of two root powder extracts, paeony and licorice, we have studied its actions and those of its components on skeletal and smooth muscles. The skeletal muscle experiments were performed on guinea-pig and rat phrenic nerve-diaphragm preparation using phrenic nerve stimulation and direct muscle stimulation. Smooth muscle experiments were done on guinea-pig ileum using the Magnus method to record both resting tension and responses to field stimulation. The guinea-pigs were Duncan Hartley, 300-500g. Rats were male Long Evans or Wistar, 200-500g. Both were stunned by cervical dislocation. We found (1) A large difference in time course of inhibition of contraction in smooth and skeletal muscles. In skeletal muscles the full effect develops over 20-30 minutes. By contrast in smooth muscle both resting and stimulated tension fall completely within 1-2 minutes. (2) The action on skeletal muscle is directly on the muscle, not necessarily or primarily on neuromuscular transmission. (3) The dose-response curve in skeletal muscle was found to be very steep, with a threshold around 1 mg/ml, and full inhibition around10 mg/ml. (4) Conditions for actions at lower concentrations as shown in a second abstract. These results could be consistent with synergistic actions between multiple components but also with the idea that there is a cascade of events in a regulatory network of interactions. The time course of action in skeletal muscle sometimes appears to be step-wise, which might indicate that the cascades develop with different time course in different motor units. Further experimental work is required to investigate these and other possibilities.