The monolayer systems of PS II membranes, PS II core complex particles, and the mixture of monogalactosyldiacylglycerol (MGDG) with PS II core complex particles were constructed by means of the Langmuir technique. The surface pressure and surface potential properties of these systems were analyzed. The apparent particle sizes were determined from surface pressure-area isotherms, which were 200 nm2 for PS II membranes and 320 nm2 for PS II core complex particles. The surface pressure isotherm analysis of the mixed monolayer of MGDG and PSII core complex particles shows that the mixed monolayer has good miscibility at all surface pressures. Copyright 1999 Academic Press.