Publisher Summary Polycyclic aromatic hydrocarbons (PAHs) are natural constituents of crude oil and many other petrochemical products. This chapter discusses the parent PAHs and their hydroxy-substituted metabolites and describes the Shpol'skii experiments on AT-ring and IN-ring hetero-substituted PAHs, particularly, amino- and nitro-PAHs and azaarenes. Shpol'skii spectroscopy of parent PAHs is shown to be applicable to various types of samples of ecotoxicological interest, such as sediments or biota extracts. Because of the excellent identification capacities of the technique, it can be used in a qualitative way for the identification of unknown compounds and for the assessment of high-performance liquid chromatography (HPLC) peak purity. The amount of metabolites excreted is a direct measure for the integrated uptake and that combining PAH metabolite levels with environmental levels of parent PAHs provides information on bioavailability. Nitrogen-substituted PAHs are of particular importance from an environmental toxicology point of view, and the fluorescence techniques discussed in this chapter can play a significant role in this field of research.