Asthmatic patients frequently develop wheezing after respiratory tract infection. Mycoplasma pneumoniae causes respiratory tract infections in children and in adults. The purpose of this study was to determine the frequency of recovery of M. pneumoniae from patients with asthma. Seventy-seven patients with asthma and 88 persons without asthma or any other respiratory tract disease (controls) were included in the study. Ages ranged from 8 months to 31 years. Throat swabs were taken and deposited in egg yolk broth with methylene blue in order to isolate M. pneumoniae. The bacterium was identified using inhibition of growth with homologous antiserum. The isolation rate in patients with asthma was 24.7% while that in controls was 5.7% (P < .01). The results suggest that M. pneumoniae colonizes a higher percentage of patients with asthma than controls and could possibly have induced the wheezing.