In the whole crayfish (Astacus sp.), contraction of the dactyl opener muscle may persist for many minutes in the complete absence of action potentials in the excitor nerve or muscle. Such maintained contraction has not been observed in isolated claw preparations. Generally, maintained contraction resembles catch in that the muscle holds its previous position and does not recontract if stretched. In one animal, however, the muscle continued to slowly open in the absence of nerve activity. Maintained contraction occurred in 5 of 6 whole animal preparations; in those 5 animals it occurred on 49% of trials. We could find no difference in nerve activity or muscle potentials on trials when such contraction occurred and on those when it did not. It is proposed that in the whole animal maintained contraction may be controlled by a factor which is released into the blood supply when the animal is aroused.