Bacteriologic findings of [human] 1205 episodes of pneumococcal otitis media are analyzed. Capsular types 6, 14, 19 and 23 apparently account for more than half the initial and subsequent infections of the middle ear. Initial infection apparently is related to age, and recurrent infection with pneumococci of heterologous capsular types occurs most often within 6 mo. of the initial attack. Nasopharyngeal carriage of the pneumococcal types most frequently causing otitis media may occur without causing infection, may antedate infection by as long as 13 mo. and may persist after infection for as long as 30 mo. Recurrence of infection with a given capsular type was identified following intervening infection with 1 or more heterologous capsular types. Simultaneous infection of the middle ear with 2 pneumococcal capsular types was observed in 1% of infections studied. The potential, but as yet unestablished, value of prophylactic vaccination against pneumococcal otitis media is considered.