The aqueous pendant drop has been used to determine surface area per molecule of insoluble surface active substances. A slow and continuous decrease of surface area has been achieved by the drop evaporation. The surface area per molecule of myristic acid inferred from a compression diagram (surface tension versus time dependence) has been in close agreement with that obtained by the Langmuir-Blodgett (LB) technique. The surface tension versus surface concentration isotherms (gamma-c) and the area per molecule of two calix[4]arene ligands with a different number of carboxylic groups in the hydrophilic part have been determined. It has been found that compressibility of a surface film is proportional to the number of carboxylic groups interacting with water. The surface tension decreases by 7 mN m(-1) per one carboxylic group in a molecule. The evaporation rate has been but slightly influenced by the surface films under study. (C) 1998 Elsevier Science Ltd. All rights reserved.