A series of calorimetric experiments were performed to investigate toxic action of ammonium ferric sulfate (AFS) on Bacillus subtilis, Pseudomonas putida and Candida humicola. The power-time curves of micro-organism metabolism were obtained, and the action of them by addition of AFS was studied. C humicola, B. subtilis and P. putida were inhibited completely when the concentrations were up to 320.0, 160.0 and 160.0 mu g mL(-1), respectively. The relationships between growth rate constant (k) and doses of AFS were approximately linear for three microbes, P. putida for 10.0-160.0 mu g mL(-1) (R = -0.9746), B. subtilis for 0-1 60.0 mu g mL(-1) (R = -0.9868) and C humicola for 10.0-320.0 mu g mL(-1) (R = -0.9955). The total heat dissipated per milliliter (Q(T)) for three microbes remained balance approximately during the lower doses, P pulida and B. subtilis less than the dose of 20.0 mu g mL(-1), 0.56 +/- 0.01 and 0.26 +/- 0.01 J mL(-1), respectively, C humicola less than the dose of 40.0 mu g mL(-1), 0.58 +/- 0.03 J mL(-1). The biomass and OD600 of three micro-organisms growth in the absence of AFS also were obtained. The power-time curve of C humicola growth coincided with its turbidity curve. It elucidates that microcalorimetric method agreed with the routine microbiology method. (c) 2008 Elsevier B.V. All rights reserved.