A sealed Devanathan cell probe was used to measure hydrogen permeation through a steel membrane in the presence of hydrogen-producing bacteria. Permeation current increases of 8 to 11 μA were observed during growth of these bacteria on the membrane. Growth of a non-hydrogen-producing species resulted in no significant current change. These measurements indicate that sufficient hydrogen may be generated within pure-culture bacterial films to affect some materials sensitive to embrittlement by hydrogen gas. Results of experiments designed to identify the cause(s) of the observed increase in hydrogen permeation rate suggest a synergistic effect of hydrogen and organic acids produced by the bacteria.