Using the electrochemical permeation technique, we have recorded fluctuations of the concentration of absorbed hydrogen in an Armco iron membrane during cathodic hydrogen charging in acidic solution. The fluctuations coincide quite closely with the dynamics of hydrogen bubbles at the cathode surface, which were followed both visually and by recording cathode-potential and ohmic-resistance fluctuations. The local flux of hydrogen into the iron membrane gradually decreases when there is an attached bubble growing and quickly increases when the bubble departs. An excellent correlation was found between the fluctuations of the concentration of absorbed hydrogen in the first layers of metal and the fluctuations of the cathode potential.