The present work summarises results of the electrochemical behaviour of high strength steel wires in a high alkaline medium simulating the solution present in concrete. The aim is to expose the possible factors affecting the initiation period of stress corrosion cracking, the most frequent form of failure of pre-stressed concrete structures. Cold drawn steel wires were subjected to constant stress at 70% of their ultimate tensile strength and exposed to corrosive environments in order to study the stability of the passivating layer. The effects of chloride concentration, temperature, presence of oxygen, and cavitation induced by ultrasonic waves were studied. Two different techniques (cyclic voltammetry and impedance spectroscopy) were employed to study the effects of those parameters on the formation/breakdown of the passive layer. The results show that variations in the studied parameters can provoke breakdown of the passivating layer even at very low chloride concentrations. Chlorides, oxygen availability, temperature changes, and vibrations have been found to be important factors in the corrosion initiation of pre-/post-tensioned tendons. (C) 2009 Elsevier Ltd. All rights reserved.