A generator for the production of radiolabelled ultrafine carbonaceous particles for inhalation and clearance studies is described. A Technegas generator in combination with Tc-99m labelling is a device used in clinical routine to investigate the ventilation of the human lung. However, under standard operating conditions the Technegas generator does not provide ultrafine particles with a stable radiolabel. The removal of saline from the Tc-eluate by an ion exchange column yielded low leaching rates of the radiolabel from the particles of below 4% within 24 h (12% under standard conditions) and guaranteed non-hygroscopic aerosol properties. Short burning times (2 s; standard 15 s) and immediate dilution of the generated aerosol into a conductive bag yielded stable ultrafine particles in the size range between 40 and 100 nm count median diameter (standard 200 nm), with a geometric standard deviation of 1.6. We adapted the generator to a bolus inhalation system, allowing regional aerosol deposition into different lung regions and appropriate clearance studies. In addition the particles can be labelled by In-111 instead of Tc-99m, extending the investigation time of clearance studies from 1 day to some weeks. (C) 2005 Elsevier Ltd. All rights reserved.