In order to study the main trends in matrix elaboration, and individual variations in these reactions, 55 human first premolars were extracted and replanted for a varying number of weeks, after which they were extracted and fixed for histological interpretation. The same extraction procedure was performed on 22 teeth which were included in the study to serve as controls. The general trend during the initial postoperative period was a degeneration and disintergration of the odontoblasts. Later, odontoblast-like cells differentiated in the pulp and wlaborated a varying quantity of reparative dentine. This development took place in the whole pulp of most immature teeth, and in the apical parts of the mature teeth. The study demonstrates that odontoblasts, under favourable conditions, can survive the trauma induced by replantation. Factors promoting a favourable response in the matrix producing processes were less pronounced and the regenerative processes more extensive, in immature than in mature teeth.