We have studied the effect of monolayer structure on dilational characteristics (surface dilatational modulus and its elastic and viscous components) of monoglyceride monolayers (monoolein and monopalmitin) spread on the air-water interface, at 20 degreesC and at pH 5 and 7. The stress response to compression-expansion sinusoidal deformation of the interface in a modified Wilhelmy-type trough with two oscillating barriers was measured as a function of deformation amplitude (within the range of 1-20% of the initial area), frequency (within the range of 1-300 mHz), and superficial density (within the range of 1-3.5 mg/m(2)). The same experimental device coupled with Brewster angle microscopy makes it possible to determine the structure and morphology of the monolayer. The monolayer structure and, especially, the conditions at which the monolayer collapses determine the viscoelastic behavior of the monolayer and the linear response of the stress to area deformation. The nonlinear viscoelastic behavior of the interface has been associated with the monoglyceride monolayer collapse. It was found that the dilatational modulus is not only determined by the interactions between spread molecules (which depend on the surface density) but that the structure of the spread monolayer also plays an important role.