We present experiments on photon‐assisted tunneling and ac Josephson effect using microwaves in an energy range 1.05<h&ngr;<2.2 meV of the same order of magnitude as the superconducting gap 0.6<2&Dgr;<4 meV. We show that, whereas the photon‐assisted tunneling shows no anomaly in this region, the amplitude of the Josephson steps is strongly affected by the Riedel anomaly. Furthermore, the results under strong irradiations show an indirect evidence of a decrease of the gap value by the creation of quasiparticles.