Despite the utility that energy diagrams have as a teaching and learning tool, a survey of their use, in seven popular Biochemistry textbooks, reveals that there is certain confusion around this topic. In our opinion, this confusion arises from the reluctance of authors to consider and indicate the conditions under which the reaction being represented occurs. For an enzyme-catalyzed reaction, it should be stressed that, under conditions where the overall reaction is spontaneous, each elementary step must exhibit a negative free energy change, and this must be properly reflected in the progression profile of the reaction. (Contains 3 figures and 1 footnote.)