From an efficacy viewpoint the study must be sensitive enough to discriminate between spacers. For a study to have assay sensitivity at least two non-zero levels need to be studied and one dose level needs to be shown to be superior to the other. Consequently, the proposed study design to assess “improvement of spirometric parameters” does not comply with the regulatory requirements3-5 and the state of the art,2 consisting of the estimation of the relative potency. Furthermore, the authors have neither compared the results statistically nor predefined the acceptance range to conclude that both VHCs are equivalent. Therefore, it is not possible to conclude that “both of the VHCs tested were suitable for use in the delivery of salbutamol.”1 The new VHC should be compared properly to be used and it should be used only with those pMDIs investigated.