The response of maxillary tissues to mucoperiosteal manipulation at different ages was studied microscopically early after operation and at maturity. Thirty-two Beagles were divided into three experimental groups, a sham-operated group and a control group. At the age of 6, 16 or 25 weeks in the experimental groups an elliptical mucoperiosteal flap was excised in the midsagittal region of the palate, relaxation incisions were made and the mucoperiosteum was elevated and closed in the midline leaving two areas of denuded bone adjacent to the teeth. The animals were killed 1, 2 or 3 weeks after the operation or at the age of 37 weeks and serial sections of the jaw tissues were examined. Two weeks after the operation, scar had formed, its lack of elastic fibres indicating a more rigid type of tissue. The palatal bone showed rapid trabecular deposition. Cervico-palatal and apico-buccal bone resorption in the alveolar socket indicated medial tipping of the teeth. The different soft tissue composition persisted until maturity. In the areas where scar tissue had developed, attachment by means of Sharpey's fibres from the mucoperiosteum to the palatal bone was found at the age of 37 weeks. Thus the different mechanical properties of scar tissue adjacent to the teeth and its attachment to the palatal bone may influence the growth and development of dento-alveolar structures.