The aim of this open, randomized, crossover study was to compare the inhaled mass of budesonide suspension delivered by nebulization, using constant output, breath-synchronized, or pulsed jet nebulization techniques. The inhaled mass was defined as the amount of drug deposited on a filter between the inspiratory port of the nebulizer and the face mask or mouthpiece used by the subjects. The breath-synchronized nebulization delivered aerosol during the whole inspiration, whereas the pulsed nebulization was adjusted to deliver aerosol for up to 1 sec from the start of inspiration. Budesonide suspensions, 2 mL of 0.5 mg mL(-1), or 2 mL of 0.25 mg mL(-1), in single-dose respules, were used (AstraZeneca R&D Lund, Lund, Sweden). Eleven children (7 boys, age range 2.5-5.8 years) with either a clinical suspicion or a confirmed diagnosis of asthma and 11 healthy adolescents and adults (6 male, age range 13-52 years) were enrolled. With constant output nebulization, the median inhaled mass of budesonide was about 17.6% (range 9.6-21.2%) of the nominal dose (i. e., dose of drug in the respule per label claim) in adolescents and adults, and 18.1% in children (15.7-21.4%). With pulsed nebulization the median inhaled mass increased to 23.4% (22.0-28.1%) in children and to 32.8% (24.8-38.0%) in adolescents and adults (P < 0.001). With breath-synchronized nebulization median inhaled mass increased to 30.1% (21.7-28.1%) in children, but was unchanged (30.8%, 27.0-38. 0%) in adolescents and adults. The mode of nebulization (i.e., constant or breath-synchronized) had a statistically significant effect on the inhaled mass in children and adolescents or adults (P < 0.001). There was a statistically significant difference in inhaled mass between the breath-synchronized and pulsed nebulization in children only (P < 0.05). The results support the use of breath-synchronized but not pulsed nebulization with conventional nebulizers. The results of pulsed nebulization in children warrants further clinical studies.