An in vitro method has been described and refined previously for the performance evaluation of valved holding chamber (VHC)-facemask systems. The purpose of this study was to evaluate the delivery efficiency of three commercial VHC-facemask systems: AeroChamber Plus Flow-Vu VHC with ComfortSeal facemask (ACP-FV); OptiChamber Diamond VHC with LiteTouch facemask (OCD-LT); Vortex VHC with Felix Frog facemask (VTX-FR) at simulated pediatric conditions. The study comprised of standardized methods to evaluate VHC-facemask seal leakage against a soft anatomical model (SAM0) and evaluation of delivered dose under an age-specific pediatric breathing pattern which was simulated using an ASL Servo Lung. The results showed that the OCD-LT system formed an effective seal at both application forces (%leakage = 47.4% at 1 lb and 46.5% at 4 lb), whereas the ACP-FV system achieved an effective seal only at high application force (%leakage = 89.8% at 1 lb; 55.6% at 4 lb). The VTX-FR system did not achieve an effective seal in any test condition. Facemask seal leakage reflected delivery efficiency. The ACP-FV system had good delivery efficiency (%delivered dose = 38-43%) at high application force (4 lb) but poor delivery efficiency (%delivered dose = 0.7-1.8%) at low application force (1 lb).The OCD-LT system resulted in the most consistent delivered dose even at low application forces (%delivered dose = 35-42% at 1 lb, 41-47% at 4 lb). When the VHCs were tested without facemask (complete seal) they all produced a good delivery efficiency (%delivered dose; 45-55 for OCD, 41-49% for VTX, and 55-58% for ACP).