Hysteresis of electrical resistance hydrogen (deuterium) content relationship in the alpha + beta two-phase region of the Pd-H(D) system measured by a gas phase method was found by Sakamoto et al. [20,21], and subsequently verified and extended to Pd alloy-H(D) systems by Kibria et al. [22-28]. However, the evidence of this phenomenon is not reliable because the resistance was measured from one sample and the hydrogen content was determined from other samples in the same vessel. In this paper, it is proposed that the 'hysteresis' is attributed to the inequality of plateau pressures between these two sorts of samples during the alpha <-> beta phase transitions of the Pd-H(D) and Pd alloy-H(D) systems. Some phenomena accompanied are also discussed on this basis. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.