An in vitro phagocytosis assay of adherent cells of 12 palatine tonsils (7 children's and 5 adults' cases with persistent angina) was performed by use of flow cytometry (FCM), using fluorescent latex particles (FLP). The mean value of the percentages of phagocytic cells in the children's group (81.4%) was higher than that in the adults' group (64.0%). In addition, separate immunocytochemical stainings with each antibody--Anti-Leu-M5, OKDR, OKT6, S-100, and lysozyme--were made on smear preparations of a child's and an adult's tonsillar adherent cells after incubation with FLP. By use of the light microscope, the percentages of phagocytic cells in relation to positive cells for each antibody were calculated. The lysozyme positive cell proved to have the highest percentage of phagocytic cells. Then, the average number of phagocytized FLP in one positive cell for each antibody were calculated. With regard to the lysozyme positive cell, this cell proved to have the highest average number of FLP.