Sea-urchin sperm flagella in a state of rigor were reactivated by rapid photolysis of caged ATP. After a time lag of 11-17 ms, all bends in the axonemes present during rigor began to be propagated towards the tip as if their propagation had not been interrupted. This result suggests that the site-specific activity of dyneins along the length of the axoneme is preserved even during rigor states when ATP is absent and that regulation of the activity can be restarted immediately with a new cycle of ATP turnover. During the starting transient, pre-existing rigor waves in the distal region were propagated without a change in the maximal shear angle until they disappeared at the tip. This was more evident when the rapid reactivation was triggered in high-viscosity solution, in which only the form of new bends was greatly affected by viscous load. After reactivation, the velocity of microtubule sliding increased and reached a plateau within 28 ms. This time course reflects the rate of force generation by dynein in situ.