AbstractThe First International Workshop on T‐cell colonies in semisolid media has released some important applications of the method: (a) it should be a very useful tool for the study of the different steps of T‐cell differentiation and their control mechanisms; (b) it may provide methods for the induction and initial cloning of functional subsets of mature T cells before subsequent expansion in liquid culture; (c) such cloned T cells may be used not only as a source of functional cells and lymphokines, but also to screen otherwise undetected subgroups of the major histo‐compatibility complex as well, hopefully for immunotherapy of malignancies and autoimmune or infectious diseases; (d) the study of lymphocyte colony formation should be complementary to investigations dealing with other lineage precursors (CFU‐GM, BFU‐E, CFU‐E, CFU‐Meg) for the monitoring of hemopoiesis in a variety of immunohematologi