Exsituphotoacoustic thermal‐wave imaging of hydrogen electropermeated in a titanium and stainless steel (AISI 304) foil has been performed. Both the magnitude and phase of the complex amplitude of the photoacoustic signal have been investigated. The results show a new phase (TiH2) in the case of titanium and typical blisters in the case of stainless steel; both could be imaged deeply below the sample surface. ©1995 American Institute of Physics.