Inhalation of slightly hyperosmolar solutions may result in asthma attacks. "Evaporation" and hence increase of the concentration of the aerosol in continuous atomisation by ultrasound has been known for a long time. The present study aimed at finding out to what extent an osmolarity increase can be detected even with commercial home inhalation devices with an inhalation period of between 3 and 5 minutes. We examined the following instruments: Heyer Sekundant, Bird-Mark 7, Respirator IPPB (supplier: Stephan) Pari-Inahalierboy, Heyer-Prodomo and the compressed-air driven inhalators FT 51 (Heyer) and the ultrasound device US-77 supplied by Heyer. Osmolality was measured with the osmometer Osmomat-030 supplied by Gonoteck. We atomised a mixture of 5 drops Berodual with physiological saline solution and isotonic brine (salt water) from the German spa Bad Ems. All inhalation devices showed after a short time an increase in osmolarity that was lowest with the Inhalierboy and Heyer Prodomo. The Heyer Sekundant and Bird-Mark 7 models showed increases that were a cause for concern. It is recommended on the basis of the results obtained that suppliers should state on their inhalation equipment not only the droplet size and aerosol density but also the increase in osmolarity on atomisation of a reference substance after 3 or 5 minutes, respectively. It would be desirable, in the interests of safe therapy, that the data given for an inhalation equipment should include over and above the usual characteristics the increase in osmolarity per unit of time under defined environmental conditions (see above) on atomisation of a reference solution.