The dependence of the yield stress of vacuum-annealed and hydrogen-purified iron polycrystals on neutron dose and annealing temperature and the influence of these two parameters on the effect of static strain-ageing has been investigated. The radiation hardening was found to depend sensitively on the interstitial impurities N and C. This may be explained by both a nucleation of precipitation and a trapping of the impurities at radiation produced intrinsic defects. The radiation enhanced precipitation predominates in the relatively impure iron samples at low doses and may be eliminated by annealing at 190 °C. The trapping becomes effective at higher doses or in higher purity iron. Below 400 °C two recovery stages for the yield stress are observed, one between 200 and 260 °C and the other between 320 and 400°C; these may be explained by the detrapping of N and C respectively. The static strain-ageing was found to be reduced by neutron irradiation. It reappears after annealing at temperatures at which the precipitates are thought to be redissolved and the C and N atoms to be detrapped.