The regeneration of the cerebellum in Xenopus laevis (Daud.) tadpoles operated at the stage 49 (according to Nieuwkoop e Faber) by ablation of the whole right rhomboidal lip, has been studied. 50 animals were operated. Some were sacrificed after 1-3-5-7-10-15-20-25-30-45 days, the others 1-2 months after the metamorphosis (3-4 months after having been operated). The results have shown that the regenerative capacity of the cerebellum in tadpoles of Xenopus laevis at stage 49, is very high and it takes place with the same mechanisms which have been shown in the regeneration of the mesencephalon. In fact we can distinguish three phases: 1. a migration phase, during which some elements of the residual region lying in the ependymal layer migrate into the operated side and form a thin newformed wall; 2. a multiplicative phase, which results in a gradual thickening of the new, ventricular wall; 3. a differentiative phase, characterized by the gradual differentiation of the neuroblasts costituting the regenerated region. The Purkinje neurons are the first which are differentiated. One month after the metamorphosis the regeneration is very remarkable and every cellular layer of the cerebellum can be distinguished. Nevertheless only in a few cases the volume of the regenerated side is the same as the intact one.