Measurements of internal friction and Young's modulus as a function of temperature and 13.7‐Mev deuteron bombardment flux are reported for polycrystalline tungsten. A dislocation‐relaxation peak in the internal friction as a function of temperature is observed. The peak height is found to be reduced by irradiation. The background internal friction decreases and the modulus increases with bombarding flux. The experimental results for modulus change with bombardment is shown to fit a simple dislocation pinning model reasonably well. The effect of immobile radiation induced vacancies on Young's modulus in tungsten is observed to be −0.44% per atomic percent of vacancies compared with Dienes' prediction of −1.0%.