[Thymosin activity in thymic fibroblast culture fluid]

Cultural media from pure transplantable strains of guinea pig thymic stromal fibroblasts increase the number of murine O-antigen bearing bone marrow cells, i. e. as thymosin. In the course of cultivation a more or less constant thymosin-like factor level can be maintained by changing the medium. It is thus shown that at least some thymosin-active components are synthesized by thymic fibroblasts.