Basophilic granulocytes and mast Cells of different species have been reported to originate from thymocytes and other lymphocytes. These observations were recently confirmed when evidence was given that thymic antigen is present on rabbit basophilic. In the study reported here, human leukocytes were tested by the immunofluorescence technique and the immunoelectron‐microscopy technique to ascertain whether a human lymphocyte antigen (HTLA) could be detected on their surface, We could demonstrate the presence of HTLA on lymphocytes but not on basophilic granulocytes, nor on mast cells in Cryostat secretion of various tissue