We compared terbutaline administered through an 80-mL, 10 X 3.2-cm tube spacer versus a conventional metered-dose inhaler in 34 asthmatic patients, aged 8 to 16 years. In this double-blind, single-dose study, three groups of children (spacer active, conventional active, and placebo) were assessed clinically and with spirometry before and at one-half hour intervals for two hours after therapy. One investigator taught inhaler use and monitored patients' errors in technique. Compared with placebo, terbutaline delivered by either the tube spacer or the conventional inhaler significantly improved pulmonary function from one-half to two hours after treatment. Both the spacer and conventional inhaler were equally effective in improving pulmonary function from the baseline state. Only 4/34 (11.7%) children used both inhalers without any error. Adverse effects were mild, transient, and infrequent and did not differ between the groups. Terbutaline aerosol, whether delivered by the tube spacer or conventional actuator, provides effective bronchodilation for children with asthma, in spite of frequent errors in technique of inhaler use.