The Spacehaler (Evans Medical Ltd, Leatherhead, U.K.) is a new, compact, inhaler device containing the same aerosol canister as a conventional metered dose inhaler (MDI). However, the design of the Spacehaler has been shown to reduce the velocity of the aerosol, thus reducing the proportion of non-respirable particles delivered to the patient. This study compared radioaerosol deposition patterns following inhalation of 250 micrograms of beclomethasone dipropionate from the Spacehaler and a conventional MDI (Beclazone, Norton Health Care, Harlow, U.K.). After rigorous in vitro validation of the radiolabelling technique, 12 asthmatic subjects (seven men aged 20-69 years, mean baseline FEV1 2.59 1 (SD 0.55 1) received one dose of 99mTc-labelled beclomethasone dipropionate 250 micrograms via either a Spacehaler or MDI on each of two study days in a randomized cross-over manner. All subjects had been taught the required inhalation technique before the dose was administered. Inhalation details were recorded using a spirometer connected in series with the device. Lung and oropharyngeal depositions were measured by gamma scintigraphy. The mean percentage of the metered dose deposited in the lungs was 23.0% (SD 8.3%) for the Spacehaler and 12.8% (SD 6.8%) for the MDI (P < 0.01). However, there was no significant difference in the distribution patterns within the lungs between the two devices. Oropharyngeal deposition was significantly lower (P < 0.01) for the Spacehaler than for the MDI [mean (SD) 27.9% (16.4%) and 73.6% (8.7%), respectively] whilst the percentage of the metered dose remaining on the Spacehaler actuator was significantly greater than that on the MDI actuator [mean (SD) 48.0% (11.8%) and 12.4% (8.5%) respectively, P < 0.01]. There was evidence from the inhalation recordings that some patients experienced the 'cold Freon effect' whilst using the metered dose inhaler which may have contributed to the lower lung deposition seen with this device. This study demonstrates that the proportion of a 250 micrograms dose of beclomethasone dipropionate that is delivered to the lungs is significantly greater with the Spacehaler than the MDI. The Spacehaler also reduces the proportion of the does that is deposited in the oropharynx to less than half that observed with the MDI, and reduces the total dose of drug received by the patient.