There has been a worldwide increase in the incidence of asthma, and the disease has greatly impacted the public health care system. Chlamydia pneumoniae has been reported as a possible contributing factor in asthma. The organism has been detected by polymerase chain reaction (PCR) in bronchial tissue, but there has been no direct evidence of viability. To determine the frequency of viable Chlamydia in children, blood and bronchoalveolar lavage were collected from 70 pediatric patients undergoing flexible fiberoptic bronchoscopy. Forty-two of these patients had asthma, whereas the remaining patients had various respiratory disorders. Fifty-four percent (38) of the bronchoalveolar lavage samples were PCR-positive for Chlamydia, and 31% (22) of the PCR-positive samples were positive when cultured on macrophages. Twenty-eight samples (40%) and 14 samples (20%) of the PCR- and culture-positive samples, respectively, were from patients with asthma. Culture of the blood samples revealed that 24 (34.3%) of 70 were positive for Chlamydia compared with 8 (11%) of 70 matched nonrespiratory control subjects (p < 0.01); 17 (24%) of the positive blood cultures from the respiratory group were from patients with asthma. Elevation of total IgE was strongly associated with lavage culture positivity for Chlamydia. We therefore conclude that viable Chlamydia pneumoniae organisms are frequently present in the lung lavage fluid from this cohort of predominantly asthmatic pediatric patients.