The equilibrium shapes of lipid monolayer domains are normally determined by the balance between the interface (line tension) energy and the long-range electrostatic repulsion between lipid dipoles. When an external electric field acts on the monolayer, a third energy term affects the domain shapes : the energy of the dipoles in the external field. We study the effects of a static field on harmonic shape transitions and of a periodically varying field on the dynamics of a distorting lipid domain.