Objective: To determine if aerially spraying a biological pesticide was associated with an increase in the symptoms or change in the Peak Expiratory Flow Rate of children with asthma. Methods: A pre/post matched pairs cohort design was used. Children living in the spray zone were matched with children outside of the spray zone. Peak Expiratory Flow Rates, asthma symptoms and non-asthma symptoms were recorded in diaries. Results: There were no differences in asthma symptom scores between subjects and controls, neither before nor after the spray; nor were there significant changes in Peak Expiratory Flow Rates for subjects after the spray period.