The nonlinear spectroscopic technique of second-harmonic generation was used to study the surface properties of bulk and microlayer seawater samples. It was found that the majority of the surface active components present in the seawater were present in the microlayer sample. Increases in film pressure correlated with increases in the second-harmonic generation signal for the microlayer samples studied. This indicates that the second-harmonic generation technique may be used to noninvasively study and determine the surface properties of seawater. ¿ American Geophysical Union 1988