The review by Lee and Pyun, which was published recently [Electrochim. Acta 50 (2005) 1777-1805], provides a comprehensive survey of the anomalous behaviours of hydrogen transport in hydride-forming electrodes, with particular emphasis on hydrogen extraction under the impermeable boundary condition during potentiostatic current transients. Some theoretical derivations presented in the above review, as well as the validity domains of theoretical results obtained by Lee and Pyun are discussed in these comments in terms of potential step amplitude, interfacial reaction mechanism, electrode kinetics and influence of Ohmic drop. In particular, the concepts of 'constraint by constant concentration', 'constraint by Butler-Volmer behaviour' and 'constraint by hydrogen transfer of absorbed state to adsorbed state' used by Lee and Pyun to discriminate between the boundary conditions at the electrode surface during hydrogen extraction are examined thoroughly in these comments. The 'transition of the boundary condition at the electrode surface during hydrogen extraction' is also discussed, as well as the influence of Ohmic potential drop on the chronoamperometric responses to large-potential steps. (C) 2005 Elsevier Ltd. All rights reserved.