Quinone oxidoreductases are a class of membrane enzymes that catalyse the oxidation or reduction of membrane-bound quinols/quinones. The conversion of quinone/quinol by these enzymes is difficult to study because of the hydrophobic nature of the enzymes and their substrates. We describe some biochemical properties of quinones and quinone oxidoreductases and then look in more detail at two model membranes that can be used to study quinone oxidoreductases in a native-like membrane environment with their native lipophilic quinone substrates. The results obtained with these model membranes are compared with classical enzyme assays that use water-soluble quinone analogues.