We have investigated the mechanical response of silicon microresonators exposed to electron- and ion-beam irradiation. The microresonators were single-crystal silicon structures consisting of beams similar to 0.7 mu m wide, and having preirradiation frequency of 48 kHz and Q(-1) of 2.5x10(-5). For the electron-beam experiment, microresonator response was measured after 10 min irradiations with 10 keV electrons, for beam currents ranging from 2 to 20 nA. The frequency shows a monotonic increase with electron dose, while the Q(-1) shows a peak versus dose. For the ion-beam experiment, the microresonator was irradiated with 3.5 keV Ar+ ions for timed intervals up to 10 min. The microresonator frequency and Q(-1) exhibit extrema versus irradiation time. These mechanical-response changes are significant for both electron- and ion-irradiation experiments, with frequency shifts similar to 0.1% and Q(-1) changes of a factor similar to 3.