A new anticholinergic aerosol containing 0.5mg ipratropium bromide dissolved in 1mL of solution has been produced with the purpose of decreasing nebulization time for patients compared to the traditional formulation which is twice as voluminal (0.5mg/2mL, Boehringer-Ingelheim, France). The aim of this study was to compare aerosol characteristics (inhaled mass, particle size distribution and nebulization time) of these two formulations of ipratropium bromide, nebulized alone and with terbutaline (5mg/2mL, Astra Zeneca, Sweden), to determine whether the new formulation was equivalent to the old one. Four different jet nebulizers were used: PariLC+, Atomisor NL9M, Sidestream and Mistyneb. Statistical analysis of the results showed that for all types of nebulizer, the inhaled mass of ipratropium bromide 0.5mg/1mL was significantly lower than the inhaled mass of ipratropium bromide 0.5mg/2mL, and that there was no statistical difference between the inhaled mass of ipratropium bromide 0.5mg/1mL+terbutaline 5mg/2mL and the inhaled mass of ipratropium bromide 0.5mg/2mL+terbutaline 5mg/2mL. The study also showed that the new formulation of ipratropium bromide (0.5mg/1mL) mixed with terbutaline allowed a 26% decrease in nebulization time compared to the old formulation (0.5mg/2mL) mixed with terbutaline without changing aerosol characteristics (inhaled mass and particle size distribution). This leads to the conclusion that a 2mL minimum volume is required for nebulization, and that nebulization of ipratropium bromide 0.5mg/1mL alone must be avoided.