The electrochemical frequency modulation EFM technique provides a new tool for electrochemical corrosion monitoring. EFM is a non-destructive technique as electrochemical impedance spectroscopy (EIS). EFM technique was used in comparison with the traditional do and ac techniques. Results obtained by EFM technique were shown to be in agreement with other electrochemical techniques. With EFM technique, a corrosion rate can be obtained instantaneously in very short time which makes this technique ideal in online corrosion monitoring. New synthesized thiourea derivative named 1,3-diarylidenethiourea (DAT) was examined as a new corrosion inhibitor for iron in 1 M hydrochloric acid solution. (c) 2006 Published by Elsevier Ltd.