Fourteen asthmatic children, aged 7.9 to 18.0 years (mean, 11.3 years), recorded peak expiratory flow rates three times a day at home for four weeks in an attempt to improve perception of their airway obstruction. Pulmonary function tests were performed and a subjective severity score was recorded before and after this period. The accuracy of the parents' perceptions of their child's airway obstruction was also assessed. These children were unable to accurately predict their degree of airway obstruction, and no improvement in prediction was seen following the learning period. Parents' perceptions of the child's airway obstruction were also inaccurate. Recording of peak expiratory flow rate at home did not improve the child's perception of his asthma. Rational management of troublesome asthma requires the use of an inexpensive peak flowmeter to provide continual objective measurements of lung function.