We have studied the surface rheology of mixed solutions of anionic polyelectrolytes and cationic surfactants.Surface elasticity and viscosity exhibit a maximum at a surfactant concentration much smaller than thatfor solutions of the pure surfactant. Foaming and foam stability were found to depend on these coefficients,although a systematic relation is difficult to establish. Still more surprisingly, the behavior of foams andfoam films is very different in these systems.