Injury of liver by ischaemia crucially involves mitochondrial damage. The role of Ca 2+ in mitochondrial damage is still unclear. We investigated the effect of low micromolar Ca 2+ concentrations on respiration, membrane permeability, and antioxidative defence in liver mitochondria exposed to hypoxia⁄reoxygenation. Hypoxia⁄reoxygenation caused decrease in state 3 respiration and in the respiratory control ratio.