We present a novel type of Langmuir trough which enables the study of monolayers deposited at the immiscible liquid/liquid interface under controlled surface pressure. Isotherms of phospholipids have been obtained both at the air/water and, for the first time, at the water/1,2-dichloroethane interfaces. The latter isotherms did not show well-defined plateau regions or phase transitions, probably due to the small size of the 1,2-dichloroethane molecules, which makes them very mobile in the surface phase. It was possible to keep the surface pressure of the monolayers constant for at least 0.5 h, which means that they can be used for electrochemical experiments, for example for the study of the kinetics of charge transfer across such monolayers.