In a placebo-controlled, randomised double blind study the healing process of three identical wounds of the oral mucosa in 30 patients was examined planimetrically, immunohistochemically and micromorphologically. One third of the wounds were irrigated without pressure every day using ozonised water (concentration 11-12 µg ozone/ml water), the next third using water, the last third remained without treatment. The application of ozonised water clearly showed an acceleration of wound healing within the first 48 hours, resulting in earlier epithelial wound closure after 7 days.