Design and working principle of a flash x‐ray system is described. A two‐stage Marx generator is used, the charging voltage is 150 kV, the stored energy 1125 J. Anode and cathode are arranged coaxially. The anode consists of a tungsten coated aluminium tube of 20 mm i.d. into which the substances to be irradiated are placed. Measurements of electrical and radiation parameters are described. The x‐ray dose per pulse is 400 rad, the half‐width of the pulse is 0.2 &mgr;sec and the mean quantum energy 44 keV. An example for the application of the system in microsecond pulse radiolysis is presented.