The purpose of this study was to determine the in vitro deposition of both drug (albuterol sulfate) and carrier (lactose) particles in relation to each other from a dry powder inhaler formulation using an Andersen cascade impactor (ACI) and time of flight aerosol beam spectromety (TOFABS). In addition, scanning electron microscopy (SEM) combined with X-ray microanalysis was employed to distinguish albuterol surfate from lactose. Drug particles apparently penetrated deeper into the impactor thatnlactose particles contained in the formulation. In some certain stages of impactor, drug particles were separated from lactose particles. Although the TOFABS cannot distinguish between albuterol surfate and lactose, the TOF spectra obtained from the Aerosizer would appear to be partly indicative of the interactions which exist between drug and carrier. One symmetrical TOF peak was obtaind from drug or lactose alone. The TOF peak of the drug was alwys lower than the TOF of lactose. The times obtained for each powder between experiments were hihgly reproducible and typical of material and particle size. The use of SEM-X-ray microanalysis also allowed some qualitative characterization of shape and state of association of the two components.