Infection with Chlamydia pneumoniae in Brooklyn. Of 91 children and adults with lower respiratory tract infection, 17 (18.7%) had evidence of infection with Chlamydia pneumoniae. Infection was more common in older adolescents and adults than in children. Only 3 of 8 culture-positive patients with paired sera had serologic evidence of acute infection. Two patients were culture positive over a 12-month period. Two other culture-positive patients had evidence of coinfection with other bacterial respiratory tract pathogens, which in these cases appeared to be responsible for the acute episode of pneumonia. Patterns of infection ranged from acute pneumonia to apparent chronic asymptomatic carriage, and there was no characteristic clinical presentation. Studies using cultures in other populations, including asymptomatic individuals, are needed for a better understanding of the epidemiology and clinical relevance of this organism. 