The development of a caries lesion is a dynamic process that includes frequently alternating periods of de- and remineralization, a process for which no in vitro models currently exists. The aim of this study was to develop a model which could repeatedly generate identical pH versus time curves over extended periods of time. To test the model demineralization studies on cementum/dentin were performed. Cementum/dentin blocks were repeatedly subjected to de- and remineralizing solutions delivered by a computerized pump system connected to a pH-meter and a recorder. pH versus time curves similar to those produced in plaque after carbohydrate intake were generated 18 times during 15 h followed by a remineralizing period of 9 h every day for 16 days. The intra-day and inter-day variation of the pH-cycling model were found to be low. The mineral change of the blocks was followed by 125I absorptiometry and the transmission through the blocks during the experimental period increased in average by 1.4 ± (SE) 0.18%. Microradiographic analysis of the transversal sections of the blocks confirmed the development of lesions resembling root caries