A convenient method for a precise determination of the amount of. absorbed hydrogen and its forms in metals is described. The method is based on the electrochemical measurement of the hydrogen desorption rate on both sides of a metal membrane. As an example, the desorption of hydrogen from a cathodically precharged Armco iron membrane was investigated. The analysis of the desorption rates of hydrogen revealed that up to 97.7% of the total hydrogen was reversibly absorbed in traps and that the trapping occurred mainly near the entry side of the membrane. The conventional permeation method allows only the diffusible hydrogen to be determined which in this case is only a small part of the total amount of hydrogen.