Clinical experience has often suggested that having asthmatic patients sit quietly and/or relax during asthma attacks is helpful. The present study was an attempt to provide a controlled experimental demonstration of the effect of systematic relaxation on peak expiratory flow rate in asthmatic children. Eighteen male and 18 female asthmatic children were divided into two groups matched for mean age, sex composition and asthma severity. One group of subjects underwent three sessions of modified jacobsonian systematic relaxation training, while the second group sat quietly for three sessions. Peak expiratory flow rate measures were obtained prior to and following each session. It was found that relaxation subjects manifested a significant mean increase in peak expiratory flow rate over sessions compared to a nonsignificant mean peak expiratory flow decrease for control subjects. It was suggested that these results have important implications both for the clinical treatment and the understanding of bronchial asthma.