A mathematical model was developed to estimate flux control coefficients (Co) from titration studies with specific non-competitive inhibitors. In contrast to the normally used graphical determination the model pays regard to the dissociation equilibrium (KD) that exists between inhibitor and its binding sites (Eo) as well as to an objective estimation of the initial slope. The model was used for the analysis of titration experiments where the respiration of rat liver mitochondria was inhibited with carboxyatractyloside and antimycin A. It is shown that the graphical estimation of Eo and Co lead to significant overestimation if the ratio KD/Eo is larger than 10(-4) which can be avoided by using our model.