BACKGROUND Although the efficacy of the administration of beta-adrenergic bronchodilators has been demonstrated, the best method available for the delivery of these drugs in the prehospital setting has not been defined. This paper compares the effects of administration of metaproterenol when administered by paramedics using either a metered-dose inhaler (MDI) or a hand-held nebulizer (HHN). OBJECTIVE There is no difference in the effects produced in patients suffering from smooth bronchiolar muscle spasm by metaproterenol when delivered either by a standard metered-dose inhaler or with a hand-held nebulizer. METHODS Consecutive prehospital patients complaining of difficulty breathing with clinical evidence of bronchospasm and with a history of asthma, chronic obstructive pulmonary disease, or emphysema who were not in extremis. METHODS Prior to the administration of metaproterenol, a peak expiratory flow rate (PEFR) was obtained. This measurement was repeated five minutes following the conclusion of the administration of metaproterenol. Patients in Burbank, California, received the treatment using a standard metered-dose inhaler, and those in Madison, Wisconsin, received the drug using a hand-held nebulizer. Peak expiratory flow rates were compared using Student's t-tests with Bonferroni's correction. Statistical significance was set at p < 0.05. RESULTS Data were collected from 36 consecutive patients by the paramedics of the Burbank Fire Department and from 32 consecutive patients by the paramedics of the Madison Fire Department. For the metered-dose inhaler group, the mean value for peak expiratory flow rate for the pre-treatment test was 95.4 +/- 88.1 l/min, and after treatment was 109.4 +/- 89.3 l/min (p < 0.001). For the hand-held nebulizer group, the mean value for peak expiratory flow rate before the administration of the metaproterenol was 96.1 +/- 76.3 l/min and following the treatment was 149.1 +/- 92.9 l/min (p < 0.001). The mean values for the differences between the control peak expiratory flow rate and the post-treatment peak expiratory flow rate for the metered-dose inhaler group was + 140.0 +/- 27.4 l/min, and for the hand-held nebulizer group was + 53.0 +/- 69.1 l/min (p < 0.003). CONCLUSIONS In the prehospital setting, the administration of metaproterenol using a hand-held nebulizer is more effective than delivering the drug using a metered-dose inhaler. The hand-held nebulizer is easier to use and delivers a higher dose of the drug than is convenient using the metered-dose inhaler.