The effects of microwave radiation on the vortex modes of Josephson tunnel junctions have been examined. Current steps are induced on the resistive branches at voltagesV=(n/m)(h&ngr;/2e) wherenandmare integers and &ngr; is the frequency of the incident radiation. The system we have studied is a well‐defined one in which vortices undergoing periodic motion interact with the periodic perturbation of the microwave radiation. Vertical steps are induced when resonance occurs.