The electrostatic wave in a plasma may be amplified parametrically by applying a pump power at microwave frequencies. The theory of the parametric interaction between the electrostatic wave and a guided electromagnetic wave is presented, and the gain parameter is derived in terms of the pump power. The pump power required to observe the effect of the pumping at microwave frequencies is calculated to be orders of magnitude less than the optical power required to produce the Raman effect in plasmas.