Reflection nebulae (RNs) are objects of SPECIAL INTEREST because they provide an opportunity to explore the interaction of a single star with a region of high density ISM.They are bright enough to permit a detailed spectroscopy of the emission by IS dust and gas . In addition, the characteristics of the stellar radiation incident can vary from object to object (O/B to M stars), allowing tests of specific models for the excitation of different IS species. Our proposal will use ISO to study a sample of RNs illuminated with widely varying temperatures. We propose to obtain: - complete 2.5-200 um spectra for a subset of RNs with varying stellar temperature. This is the HEART OF THE PROPOSAL. - 3-200 um broad band energy distributions of the emission for all RNs. - measurement of the gas heating efficiency for a subset of RNs, by varying(i) the IRRADIATION SPECTRA (O/B to M stars) and (ii) the FLUX INTENSITY (different distances from the star in a given RN). Specifically, we want to: - confirm or deny the PAH hypothesis;if confirmed, make a more specific identification of the molecular species and correlate their ionization and dehydrogenation states with the stellar irradiation. - search for C60 molecules or ions. - look for spectral features that could identify the particles emitting by temperature fluctuations in the 20-100 um range, because, presently, we know NOTHING on their chemical nature. - determine whether there is a cut-off in the exciting star temperature underwhich the gas heating efficiency drops, as expected if the heating mechanism is photoelectric effect.