Objectives: Examination of the effect of Rapid White (Natural White Inc., USA) on the demineralisation behaviour and the surface morphology of human enamel. Methods: For the demineralisation study 10 selected enamel surfaces of extracted third molars were cut into two equal halves (test and control). The test surfaces were exposed to Rapid White gel twice a day for 12 minutes (36 times in all). The bleaching gel was removed from the teeth and a whitening toothpaste was applied for 5 minutes according to the manufacturers recommendation. The teeth were slightly brushed with a soft tooth brush. Following artificial lesions (0,1M Na-acetate buffer (pH 4,9) in 6% HEC, 9 days) were created on the test and control surfaces within previously prepared windows (1x3mm). Longitudinal 100µm-sections were produced after demineralisation. The depth of the lesions was estimated under polarised light after imbibition in ethanol. Further 5 enamel surfaces were investigated by SEM. Epoxy resin replicas of these surfaces were prepared before and after bleaching to enable the comparison of the very same area. Results: A moderate change in colour of the bleached specimens was evident. PLM: There was found a significant lower lesion depth of the bleached (50 ± 8µm) compared to the non-bleached (64 ± 9µm) surfaces. SEM: Magnification of at least 3000x revealed a loss of material: Rougher surfaces and local enhanced porosity were indicated after bleaching. Flat scratches disappeared, deeper scratches and defects were roughened and partially expanded . Enlarging of existing fractures and new clefts were proved. Conclusion: Despite the observed microstructural alterations of the enamel surface the demineralisation was reduced significantly after bleaching. Further studies are needed to confirm if these results are related to the use of the whitening toothpaste which follows the application of the whitening gel.