We study cotunneling in a double-junction Coulomb blockade device unde
r the influence of time-dependent potentials. It is shown that the ac
bias lends to photon-assisted cotunneling that in some eases may domin
ate the transport. We derive a general nonperturbative expression for
the tunneling current in the presence of oscillating potentials and gi
ve a perturbative expression for the photon-assisted cotunneling curre
nt.