We designed a new, washable, and collapsible bag spacer (the Siriraj Spacer) for use with metered-dose inhalers (MDI) by Thai asthmatic patients. The Siriraj Spacer consists of a mouthpiece, a front panel to which any type of MDI could be attached and a collapsible 800 mL ringed-plastic bag. Fifteen asthmatic children (6-13 years of age) were enrolled into a randomized, double-blind, triple crossover study (spanning a period of three days) to compare the clinical effectiveness of the Siriraj Spacer with that of the Volumatic Spacer (Glaxo, Inc., Research Triangle Park, NC, U.S.A.) and with the use of MDI alone. Medication used with the active method of administration was 2 puffs of albuterol (100 micrograms/puff) while 2 puffs from placebo MDI were used with the other two methods in succession. All children were stable asthmatic patients, and had been instructed how to use MDI properly by an open mouth technique just before the initiation of the study. Spirometry (FEV1, FVC, PEFR, and FEF25-75%) was followed for six hours after the administration of albuterol. The baseline FEV1s of the three study days were within 50% to 70% of the predicted values (with baseline variability of less than 20%). Data were expressed as percentage of improvement from baseline. By an analysis of variance with repeated measures, no significant differences were observed between pulmonary function data obtained with any of the three methods of bronchodilator administration (P > .05) at any time point throughout the 6-hour period.(ABSTRACT TRUNCATED AT 250 WORDS)