Although there were cross-reactions between A denticolens (DMS 20671) anti-serum and the twoActinomyces species examined, the antigens of A denticolens (DMS 20671) were clearly immunolabelled with 1:128,000 diluted antibodies on the clumps in the tonsillar crypts (Fig 1B-a). The other bacteria were not immunostained even with a dilution of 1:64,000 or less. Consequently, immunopositive antigens were detected in all 11 tonsils (100 per cent) with actinomycotic clumps identified in the tonsillar crypts: 10 (90.9 per cent) palatine tonsils and 6 (54.5 per cent) lingual tonsils. The immunolabelled areas on the bacterial cells were almost consistent with the area positively stained using both Gram's and Grocott's methods. Interestingly, positive antigens were detected in the parenchymal area in contact with the tonsillar lymphoepithelial symbiosis and antigens were phagocytosed by the macrophages in the tonsils (Fig 1B-b).