The treatment of both the bronchoconstriction and inflammatory aspects of asthma simultaneously by a single pressurized metered dose inhaler (pMDI) represents a significant advance in convenience to the patient. However, a valved holding chamber (VHC) may still be needed to reduce the coarse component of the dose that is likely to deposit in the oropharyngeal region, and a small sized device may offer significant advantages to the patient from the standpoint of compliance with therapy. VHCs representing small (adult AeroChamber Plus with mouthpiece, 149-mL) and large (Volumatic, 750-mL) devices have been compared in an in vitro evaluation with Seretide/Advair (hydro-fluoro alkane [HFA]-formulated fluticasone propionate [FP = 125 microg/dose] and salmeterol xinafoate [SX = 25 microg/dose]) by Andersen Mark-II eight-stage impactor operated at 28.3 L/min following compendial methodology. Fine particle fraction, based on the size range from 1.1 to 4.7 microm aerodynamic diameter, from either large or small VHCs with either component (69-79%) was similar [p > or = 0.08], and significantly greater than that from the pMDI alone (approximately 40%) [p < 0.001]. Fine particle dose emitted by the VHCs for SX (8.2 +/- 0.8 microg for the AeroChamber Plus and 7.7 +/- 0.5 microg for the Volumatic) were comparable, and also similar to the fine particle dose delivered by the pMDI when used without a VHC (7.6 +/- 0.6 microg). Fine particle doses for the FP component delivered by the two VHCs (46.4 +/- 3.4 microg for the AeroChamber Plus and 46.3 +/- 2.7 microg for the Volumatic) were equivalent, but were slightly greater than the corresponding fine particle dose from the pMDI alone (39.1 +/- 2.6 microg). However, this difference (approximately 20%) is close to the limit of resolution based on intermeasurement variability and is unlikely to have clinical significance, given the interpatient variability seen with inhaled drug therapy. It is therefore concluded that either of these VHCs has equivalent in vitro performance with this combination formulation in terms of the portion of the dose emitted from the pMDI that is likely to reach the receptors in the lungs.