A novel method for characterizing the electrostatic charge in pharmaceutical aerosols was developed. Electrical low-pressure impaction (ELPI) was modified and optimized to allow the measurement of aerosol particles from metered dose inhalers (MDIs) for anti-asthmatic drugs. Two commonly used MDIs, Ventolin T M and Flixotide T M , were investigated for the charging properties of their emitted aerosols. Ventolin T M aerosol was found negatively charged, whilst Flixotide T M aerosol was bipolarly charged, containing both positive and negative charged particles. The electrostatic charge measurements for both MDIs were reproducible with %CV ranging from 3.3% to 12.5% for 10 actuations from each of the inhalers. In addition, chemical assay was undertaken to obtain mass distributions of the aerosol collected inside the ELPI. Both MDIs showed that only a small amount of the drug was recovered from the submicron size range where a large amount of charge was present (negative charge for Ventolin T M and positive for Flixotide T M ). For the Flixotide T M , the majority of drug was recovered from the 1 to 10μm particles which were negatively charged. Hence, different particle size fractions of the aerosol can contribute differently to the charge which can feasibly be studied by the ELPI method.