Bleaching has been accepted as one of the methods of treating discoloured teeth. The object of this study was to assess the effectiveness of treating discoloured teeth with a dual activated bleaching system (Hi Lite) that utilises both light and chemical activation of hydrogen peroxide. The results achieved with a 19% hydrogen peroxide solution were compared with those using 35% hydrogen peroxide solution provided in a standard kit. Twenty-three university students with various complaints of discoloured teeth were treated with the bleaching system utilising both concentrations of hydrogen peroxide. Colour change was monitored by using Vita Shade Guide and a camera. The teeth were observed to be 1/2 to 2 shades lighter after each treatment session. It required one to three treatment sessions to achieve the desired results except for severe tetracycline stained teeth. There was no visible difference between the results achieved by the different concentrations of hydrogen peroxide although it took 3 to 5 minutes longer for the 19% hydrogen peroxide to effect a change in colour.