The monolayer properties of phospholipids have been well studied in recent years; however, the properties of glycosphingolipids, although of importance in cell recognition processes, have not been investigated as thoroughly. In this paper we report on the surface pressure-area, surface potential-area, and dipole moment-area isotherms of dipalmitoylphosphatidylcholine, DPPC, and the glycosphingolipids (\mathrm{G}{\mathrm{M} 1}) and (\mathrm{G}{\mathrm{TIb}}). The gangliosides exhibit expanded liquid film behavior, with measurable surface pressures detectable at molecular areas of (1.5 \mathrm{~nm}^{2}) and (2.5 \mathrm{~nm}^{2}) for (G_{M 1}) and (G_{T 1 b}), respectively. These large molecular areas are a consequence of the large headgroups of these lipids and their charged nature. In addition mixtures of the gangliosides and phospholipids have been studied. In the mixtures of DPPC and gangliosides a negative deviation of the surface pressure with area was observed, indicating a degree of association between the different lipids in the film. Although there have been some data published on these systems by other workers the data have been contradictory in nature. 1993 Academic Press, Inc.