A previous study of pyrene solubilized in Langmuir lipid monolayers of eicosanoic acid (EA) suggests that pyrene is localized close to the water phase (Langmuir 1992, 8, 1366). In this work, we have examined the orientation of pyrene in monolayers of EA and monolayers of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) by means of polarized light spectroscopic methods. At low pyrene concentrations, fluorescence anisotropy experiments reveal that the aromatic plane is preferentially oriented perpendicular to the normal of the monolayer. The deviation from the theoretical value expected for a perfectly planar monolayer is compatible with the existence of slow director fluctuations. The experimental results strongly suggest that the pyrene molecules at low concentrations are located between the monolayer and water, so that the aromatic plane forms an interface. With increasing pyrene concentrations, the orientation of pyrene becomes gradually disordered.