The objective of this study was to determine the output, in-vitro, solution of a concentrated solution of flunisolide from two different nebulisers under simulated breathing conditions. The BimboNeb and Nebula nebulisers were used to nebulise 2.6 mL of flunisolide solution (600 microg). Particle size was determined by inertial impaction and the total output of drug from the nebulisers under simulated breathing conditions was measured using a sinus flow pump. Two different breathing patterns were used, simulating nebuliser use by a child and an adult. The mass median aerodynamic diameter of flunisolide particles from the BimboNeb and Nebula were both 3.9 microm. With the simulated paediatric breathing pattern, both nebulisers delivered similar amounts of flunisolide (56.4 microg (s.d. 1.4 microg) and 56.1 microg (5 microg) over 5 min from the BimboNeb and Nebula, respectively). With the adult breathing pattern, flunisolide delivery from the BimboNeb was increased to 88.9 microg (3.3 microg), but delivery from the Nebula was only slightly increased to 64.6 microg (1.4 microg). With both nebulisers, little drug was released after 5 min of nebulisation. Both nebulisers delivered 9-15% of the nominal dose of flunisolide to the breathing simulator, a similar percentage to previous studies with budesonide and more than previous studies with beclometasone. Drug delivery from the BimboNeb, but not the Nebula, was affected by the simulated breathing pattern. This study suggests that drug delivery from nebulisers is dependent upon the interaction between the nebuliser, the drug and the patient.