The capabilities of the photoacoustic technique to measure small absorptivities is now well documented. This capability is now being exploited to measure nonlinear absorption in a variety of materials. The potentials of this new non-linear spectroscopic techniques are just beginning to be realized. Preliminary experiments have shown the ability to separate linear and nonlinear absorption in solids,1 several nonlinear processes in gases have been observed,2 and Raman and two-photon spectra of liquids have been obtained.3,4 All indications are that nonlinear photoacoustic spectroscopy, NLPAS, will be as fruitful a field as linear photoacoustic spectroscopy has been in the past.