The photocatalysed degradation of various selected pesticide derivatives, namely NN-Dimethyl-alpha-phenyl benzene acetamide (Diphenamid) [1], 1,2-diethyl phthalate (DEP) [2], 5-bromo-3-sec.butyl-6-methyl uracil (Bromacil) [3], 3-tert-butyl-5-chloro-6-methyluraciI (Terbacil), 2,4,5-tribromoimidazole (TBI) [4], Methoxychlor, Chlorothalonil and Disulfoton [5] as well as that of two selected priority organic pollutants, namely benzidine and 1,2-diphenyhydrazine (DPH) [6], has been investigated in aqueous suspensions of titanium dioxide (TiO2) under a variety of conditions. The degradation was studied by monitoring the change in substrate concentration employing UV spectroscopic analysis or HPLC technique and the decrease in total organic carbon (TOC) content, respectively, as a function of irradiation time. The degradation kinetics was studied under different conditions such as reaction pH, substrate and photocatalyst concentration, type of photocatalysts and the presence of alternative additives such as H2O2, KBrO3 and (NH4)(2)S2O8 besides molecular oxygen. The degradation rates and the photonic efficiencies were found to be strongly influenced by the above parameters. A toxicity test was performed for irradiated samples of few selected systems measuring the luminescence of bacteria Vibrio fischeri after 30 minutes of incubation.