The surface pressure increase in suspensions of dimyristoyl/palmitoylphosphatidylcholine (DMPC/DPPC) and dioctadecyl-dimethylammonium chloride (DODA)Cl vesicles have been investigated as a function of temperature. The surface pressure (tension), recorded on a Langmuir Balance (tensiometer) with continuous increase in temperature, changes abruptly at the gel double left right arrow liquid-crystalline transition temperature (T-m) of the vesicles. The values of T-m obtained by this fast and reproducible method are in good agreement with those determined by a variety of other techniques.