The aim of this work is to establish a quantitative relationship between the destabilization of a monoglyceride (monomyristin) monolayer at the air-water interface as a function of subphase composition (ethanol and sugar solutions), temperature, and surface pressure. The destabilization of monomyristin films has been followed kinetically by observing changes in the film area with time at constant surface pressure. It has been observed that the film stability is a phenomenon related to the cohesive forces in the film and to the interactions in the subsurface region. Film elasticity-expressed by the modulus (-d pi/dA)-is proposed as the parameter which describes this relationship. Its value has been related to the mechanisms that control film destabilization. The most common relaxation mechanisms found are desorption caused by dissolution and diffusion in the subphase and collapse caused by nuclei formation and further growth. The diffusion-controlled mechanism only appears when the him has a condensed structure and with low values of the elasticity modulus. For monolayers with a liquid-condensed or liquid-expanded structure-with high values of the elasticity modulus-the relaxation mechanism of collapse with nuclei formation appears. The values of the kinetic parameters for the destabilization can be discussed in terms of interactions between subphase and film molecules.