Using a phosphatidylcholine (PC) modified electrode, an unusual stabilization of p-benzoquinone anion radical (BQ(.-)) is observed even in a buffered solution of pH 7.0. To clarify this incorporation reaction of BQ(.-) in a PC layer, the effect of the molecular structure of the lipid was studied by constructing the PC modified electrodes with four PC derivatives; dicaproyl-, dilauroyl-, dipalmitoyl- and diarachidoyl-PC. At 25 degrees C, dilauroyl-PC with a moderate alkyl chain length stabilized BQ(.-) and allowed the approach of benzoquinol onto the surface of the modified electrode. From the pH dependence of the electrochemical responses, the incorporation mechanism of BQ(.-) with -P(O)OH was clarified. In addition to dilauroyl-PC, because dipalmitoyl-PC was found to incorporate BQ(.-) over 40 degrees C, the relationship between its incorporation and the phase transition temperature of each lipid has become clear. The correlation and the incorporation profiles were examined by measuring the oxidation of benzoquinol as well as that of BQ(.-). Also, the diffusion coefficients were determined for the lipids incorporating BQ(.-).