At low rotation speeds of a rotating disc electrode the diffusion-controlled inhibition of zinc deposition by lead acetate or tetrabutylammonium bromide emphasizes the existence of multiple steady states. With both zinc and nickel deposition, low frequency impedance measurements reveal an additional inductive loop associated with a diffusion-controlled inhibition of electrodeposition. From the relaxation time constant it has been concluded that this loop arises from a coupling between the inhibitor diffusion and interfacial processes slower than diffusion and involving, at least for zinc deposition, the slow renewal of active growth sites.