Photocatalytic degradation of two selected dye derivatives, chrysoidine R and acid red 29, has been investigated in aqueous suspensions of titanium dioxide under a variety of conditions. The degradation was studied by monitoring the change in substrate concentration employing UV-spectroscopic analysis and decrease in total organic carbon (TOC) content as a function of irradiation time. The degradation was studied under a variety of conditions such as reaction pH, catalyst concentration, substrate concentration, different types of TiO2 and in the presence of electron acceptors such as hydrogen peroxide (H2O2) and ammonium persulphate (NH4)(2)S2O8 besides molecular oxygen. The degradation rate 3 were found to be strongly influenced by all the above parameters. The photocatalyst Degussa P25 was found to be more efficient as compared with other photocatalysts. The degradation products were analysed by GC/MS analysis technique, and probable pathways for the formation of different products have been proposed.