To investigate the growth of oxide films on zirconium electrodes potentiostatic pulse measurements were carried out in 0.5 M H,SO, and 1 M HNO, in order to study dependence on the polarization potential E,, 0 < E, -c 9 V in the time scale of 1 ps < t -e 1 ks. The current density i, the total anodic charge 4 and the electrode capacity C ware measured in dependence on E, and t. The limitations of the electronic equipment have to be considered for t < 1 ms and i > 1 A cm -3. In very short times of polarization c c 1 ms a dissolution-precipitation mechanism is observed for larger potential steps. The fast dissolution of Zr4+ ions and the local breakdown cause the partial activation of the surface. Repassivation takes place after sufficient oversaturation of Zr4+, and d lg i/d lg t = -2 is observed. In an intermediate range of polarization times 50 ms < t x 1000 s the oxide growth follows the laws typical for high field mechanism: d Ig i/dig t = -1, C-l/d--lg t and l/C -I&.. The activation distance df is about 1.2 nm. For long periods of polarization, corrosion limits the evaluation of coulometric data and capacity data should be preferred. Applications for the repassivation of active surfaces formed under mechanical stress, in pits or due to radiation damage are discussed.