Only a small fraction of the dose from a pressurized aerosol inhaler reaches the lung, because most is deposited on the upper airways by inertial impaction. We have investigated the effects on aerosol deposition of two spacer devices (a 10-cm tube and a 22-cm cone) by incorporating teflon particles (mass median aerodynamic diameter, 3.2 micrometer) labeled with 99mTc into pressurized canisters. Ten subjects with obstructive airway disease inhaled the aerosol in a controlled manner from a conventional actuator alone or in combination with the tube or the cone. Radioaerosol distribution was measured using a shadowshield whole body counter. Deposition on the conducting airways was significantly improved by both spacers, but alveolar deposition was unchanged. Initial oropharyngeal deposition was reduced by both spacers in all 10 patients. We conclude that the spacer devices may have a role to play in aerosol therapy by increasing drug availability to the lung, while at the same time decreasing unwanted drug deposition in the oropharynx.