Pyridine, 1-2-dimethoxybenzene, morpholine and lindane are mineralized by the TiO2-UV process. In the studies briefly reviewed here, their intermediate products, in particular the aliphatics, were identified both to determine what are the compounds that may be left in the treated water and to increase our understanding of the photocatalytic pathways. In addition to the oxidation and cleavage of the bonds, H(Cl) atom addition (or transfer) and coupling reactions were found to occur, which illustrates the complexity of photocatalytic degradations. Moreover, a comparison of the primary products of quinoline degraded either by photocatalysis or by the photo-Fenton process (Fe ions-H2O2-UV) showed that OH° radicals are not the only active species involved in photocatalytic degradations. From the effects of adding superoxide dismutase, it was inferred thatin situ formed O2−o anion-radicals intervene chemically, possibly by reacting with quinoline cation-radicals generated via electron transfer from quinoline to TiO2.