Chickens were injected posthatching with cyclophosphamide in three different doses (total 8, 10, 11 mg). Histomorphological analysis of bursal tissue was performed up to 11 weeks of age. A probable biphasic recovery was observed in the majority of the chickens. The first phase of recovery is characterized by the appearance of solitary thioninophilic cells in reticuloepithelial follicles, followed in a few follicles by a redevelopment similar to embryonal follicular genesis. The late phase of recovery starts from week 7 on by infiltration of reticuloepithelial follicles with mature plasma cells in the manner of a peripheral lymphoid organ followed by thioninophilic lymphoid cells. The latter cells populate the follicles successively. Different transitions to normal follicles then take place. These investigations confirm observations of a reconstitution of bursal compartments starting some weeks later than the recovery of thymus, which takes place 2 weeks after cyclophosphamide treatment.