Ninety-three asthmatic patients were examined on 320 occasions for wheezing and peak expiratory flow rate (PEFR). The presence of a wheeze (either reported by the patient or found on examination) was associated with a significantly lower PEFR. Expiratory wheezing was usually accompanied by inspiratory wheezing; this biphasic wheezing was associated with a lower PEFR than only expiratory wheezing. Loudness and the high pitch of wheezing were associated with more severe obstruction. Most expiratory wheezing lasted throughout the entire expiration. Expiratory or inspiratory wheezing of high pitch, moderate to severe intensity, and spanning the entire phase of the breath was associated with a lower PEFR than wheezing without these characteristics. Although characterization of wheezing has a general relationship to the severity of airway obstruction, an objective measurement of expiratory flow rate is necessary for the evaluation of each patient's condition.