The inhibitory effects of five hydroxyanthraquinones (HAQs) from root and rhizoma of Rheum officinale Baill, a traditional Chinese medicinal (TCM) herb, on Staphylococcus aureus growth were investigated by calorimetry. The power-time curves of S.aureus with and without HAQ were acquired and the extent and duration of inhibitory effects on the metabolism evaluated by growth rate constants (k(1), k(2)), half inhibitory ratio (IC50), maximum heat output (P-max) and peak time (t(p)). The value of k(1), and k(2) of S. aureus in the presence of the five HAQs decreased with the increasing concentrations of HAQs. Moreover, Pm x was reduced and the value of tp increased with increasing concentrations of the five drugs. The inhibitory activity varied for different drugs. IC50 of the five HAQs was 4 mu g ml(-1) for emodin, 3.5 mu g ml(-1) for them, 10 mu g ml(-1) for aloe-emodin, 1000 mu g ml(-1) for chrysophanol, 1600 mu g ml(-1) for physcion. The sequence of antimicrobial activity of the five HAQs: rhein > emodin > aloe-emodin > chrysophanol > physicion. (c) 2005 Elsevier B.V. All rights reserved.