Fifty-four ears with evidence of pneumococcus (Pn) in the first acute otitis media (AOM) in 38 infants and with prolongation or recurrence of the MEF during the follow-up were observed for 7-22 months for the presence of Pn by culture or of pneumococcal antigen (Pn-ag) by counterimmunoelectrophoresis or latex agglutination methods in their MEFs. During the first three 1-month observation periods, Pn and/or Pn-ags were detected in 24% to 9% of these ears, always of the initial type/group. Later on new Pn types/groups appeared also. In two of the 9 MEFs persisting for greater than or equal to 3 months, initial Pn-ag, with culturable Pn, was repeatedly found but not for longer than 5 months. Of the 12 ears resulting in secretory otitis media (SOM) only one showed initial Pn-ag (and Pn) in the MEF of SOM. Pneumococcal type/group pattern associated with prolongation or recurrence of infection did not differ from that of initial AOM. In another series of 151 SOM ears in 97 children, Pn-ags were detected in 7 MEFs. Four of them grew Pn, each of the corresponding group. Our studies suggest that the persistence of Pn-ags in the middle ear after AOM is limited and their occurrence in the MEFs of SOM is rare. Thus, the role of the persistence of Pn-ags in prolonged, recurrent or secretory otitis media seems questionable.