The electromechanical behavior of two cross-linked strong acid hydrogels-(I) 50% sulfonated poly(styrene-b-ethylene-co-butylene-b-styrene) (S-SEBS) and (2) 69% sulfonated polystyrene (S-PS)-were studied in 0.005-0.1 M solutions of Na2SO4, Cs2SO4, (CH3)(4)NHSO4, and (C4H9)(4)NHSO4 (TBA) in a 1.6 V/cm dc electric field. Both gels bent toward the cathode when they were preequilibrated in the corresponding salt solutions. The bending angle increased linearly with time at the start and then more slowly toward a steady-state bending angle, theta(ss). The time needed to reach theta(ss) depended on the mobility of the cations, the electric field, and the thickness of each gel, but not on the salt concentration. Both theta(ss) and the initial speed of bending reached a maximum at the same intermediate salt concentration, C*, that changed little with type of salt or gel. theta(ss) decreased while the initial bending speed increased with the mobility of the cation. When the S-PS gel was preequilibrated in distilled water before the bending measurements, the gel first bent toward the anode before reversing toward the cathode in 0.065-0.08 M TBA solutions. The S-PS gel did this in none of the other salt solutions, and the S-SEBS did not reverse its bending behavior at all. The reasons for some of these results are discussed.