A new technique for the determination of the orientation distribution of a porphyrin within a Langmuir monolayer, in terms of the mean tilt angle relative to the monolayer normal and the width, is described. The technique utilizes the measurement of polarized fluorescence, excited with the electric field both parallel and perpendicular to the monolayer plane. The main difference between this technique and the existing ones [Fraaije et al., Biophys. J. 1990, 57, 965; Edmiston et al., J. Am. Chem. Sec. 1997, 119, 560; Bos et al., Biophys. J. 1995, 68, 2573.] is that the fluorophores are excited directly by the incident beam rather than an evanescent field, which greatly facilitates its application to Langmuir monolayers at the air-water interface. The technique was applied to the study of two systems with different porphyrin orientations: a Langmuir monolayer of a dihelical synthetic peptide BBC16 containing Zn(II)protoporphyrinIX and a monolayer of tetrakis (N-methyl-4-pyridil) porphyne electrostatically bound to the Langmuir monolayer of dipalmitoylphosphatidic acid. The results for the mean tilt angle are in good agreement with other relevant data in the literature for both systems. It is also shown that both systems exhibit rather narrow distributions, which makes them attractive for biophysical studies.