Cell-size distributions of human tonsillar lymphocytes (TL) and adenoid lymphocytes (AL) were determined using a computerized cell-size analyser. In comparison with peripheral blood lymphocytes, TL, and AL comprised a greater number of large lymphocytes. Child TL were characterized by an enrichment of not only B-lymphocytes but also of large lymphocytes. A decrease in the number of large B-lymphocytes with advancing age was considered to be indicative of the morphological profile of tonsillar involution.