Summary.The authors have endeavoured to adapt the classical method of extirpation, for investigating the function of a tissue, to the lymphoid system. Operative technique for the removal of lymphoid organs is described for use on guinea‐pigs and rats.In rats we found a pronounced lymphopenia lasting for three to six weeks in association with the operations. In the first days it was found to be unspecific, whereas during the remainder of the period it stands presumably in causal relation to the extirpatio