Acute toxicity of olive mill wastewaters (OMW), collected from a continuous olive mill, was evaluated in rat liver mitochondrial bioenergetics. Inhibition of respiratory activities in state 4, state 3, and uncoupled respiration are essentially mediated through partial inhibitions of mitochondrial complexes II and III. ATPase activity was considerably less depressed by OMW than ATP synthase activity (a difference of 42%). The inhibition observed on ATP synthase is mostly the result of an inhibition on the redox complexes. Ultimately, the OMW-induced loss of phosphorylation capacity was not only the result of a direct effect of OMW on the enzymatic complex (F(0)-F(1) ATPase), but also the result of a deleterious effect on the integrity of the mitochondrial membrane, which can promote an inhibition of the respiratory complexes and an increase of the proton permeability of the inner membrane.