The effect of the elastic reflexion of slow (< 2 eV) electrons from the anode and the cathode of a planar diode on the potential distribution and the voltage/current characteristic is worked out. Both the `exponential' and the `space-charge limited' regions of the characteristic are treated, and for the exponential region some new $\xi$-$\eta$ tables have been computed which include the effect of electron reflexion. The characteristic of an actual planar diode is calculated as an example and is compared with the experimentally determined characteristic. It is concluded that the elastic reflexion of slow electrons in a diode with an oxide-coated cathode has a major effect on the voltage/current characteristic and the electric field distribution. The determination of contact potential associated with the diode is also affected.