Objective: To investigate the effects of xylitol chewing gum containing calcium hydrogen phosphate and funoran (a polysaccharide extracted from seaweed) on initial enamel lesions. Methods: The clinical trial of the study was double blind. Human enamel blocks with artificial subsurface lesions were mounted in oral devices in 15 subjects. The subjects served as their own controls and were instructed to chew the three different gums, containing: (1) 79% sucrose (S), (2) 40% xylitol (X) and (3) 40% xylitol plus calcium hydrogen phosphate and funoran (X+2), 7 times daily, for a period of 1 week each respectively. Mineral content within the lesions after chewing each gum was analysed by quantitative microradiography. All data were analysed statistically using a one-way ANOVA test. Results: After chewing the gums, the amount of mineral at all depths of subsurface lesion was highest in the X+2 group, followed by the X group and then the S group. The difference between the groups was statistically significant (p 0.01), especially in the lesion body. Conclusion: Xylitol chewing gum containing calcium hydrogen phosphate and funoran significantly enhanced the remineralisation of initial human enamel lesions in situ. Keywords: calcium hydrogen phosphate, enamel subsurface lesion, funoran, remineralisation, xylitol chewing gum