Regeneration followed partial amputation of the tail fin in three representative species of teleosts. A systematic study, using histochemical methods, radioautography and transmission electron microscopy, disclosed the essentials of the natural history of regeneration of the fin soft-rays. At about 24 hours, epidermal cells had completely covered the cut edge. By the second day an apical epidermal cap was established. Beneath this cap a blastema was formed by about three days after amputation. A collagenous lepidotrichial matrix had begun to develop by 4 days after excision. Actinotrichia were first detected in the regenerates at 5 days. During these processes, the basal lamina of the epidermis played an important morphogenetic role. The cells responsible for the regenerate underwent regressive changes after form and function had been restored.