We present the theory of parametrically resonant surface plasmon polaritons (SPPs). We show that a temporal modulation of the dielectric properties of the medium adjacent to a metallic surface can lead to efficient energy injection into the SPP modes supported at the interface. When the permittivity modulation is induced by a pump field exceeding a certain threshold intensity, such a field undergoes a reverse saturable absorption process. We introduce a time-domain formalism to account for pump saturation and depletion effects. Finally, we discuss the viability of these effects for optical limiting applications.