We present Brownian dynamics simulations of the compression and expansion of monolayers adsorbed at a planar interface. The surface-active species are modelled as monodisperse spherical particles that can form particle-particle elastic bonds. The objective is to model the large compression and expansion of viscoelastic protein films investigated in Langmuir trough experiments. We determine the stress-strain response of the system and the associated microstructural changes induced by the large deformation of the interface as a function of particle adsorption energy, and bond breakability and stiffness. We also Study the effect of the velocity of compression and the type of compression (uniaxial or homogenous) on the mechanism of collapse of the adsorbed films. Furthermore, we present Simulations on complex mixed systems containing both bond-forming particles (modelling protein) and nonbond-forming particles (modelling surfactant). We find that the preferential desorption of one type of particle or the other, upon compression, is sensitive to the extent of bond breakability of the bond-forming species. (c) 2005 Elsevier Inc. All rights reserved.