Groups of mice were exposed to whole-body irradiation with moderately low fast neutron doses with 14 MeV average energy. The doses delivered to the internal soft tissues of mice were calculated. The changes in the concentrations of copper, magnesium, iron, zinc and calcium in the kidney, heart and spleen were estimated using atomic absorption spectrometry. Results revealed a significant reduction in the concentrations of these elements, 24 hours following irradiation with doses between 10 and 25 rem. Follow-up of the post-irradiation response was continued for 16 days for the 20 rem dose. A gradual increase in the concentration of the elements was noted which exceeded the pre-irradiation levels in most cases. However, by the end of the experiment, 16 days post-irradiation, some elements were still significantly below the control level.