The performance of 14 commercial jet nebulisers has been assessed; Unineb, Suremist (Unimed (UK) Ltd), Micro-Cirrus (Intersurgical Ltd), Pulmo-Neb (DeVilbiss Health Care UK Ltd), Side-Stream (Medic-Aid Ltd), Micro-Neb III (Lifecare Ltd), RespirGard (Marquest Medical Products Inc), Aeromist, Venticaire (S and W Vickers Ltd), Up-Draft II, Ava-Neb, Up-Draft (Hudson Respiratory Care Inc), Bennett/Twin, Raindrop (Puritan-Bennett Corporation). The units were operated with a high flow compressor (Maxi III, Medix Ltd) at 101/min. Performance was assessed by measuring the fraction of the initial mass of drug released as an aerosol and nebulisation time for initial drug volume of 2-6mls, and the mass median diameter and mass fraction of the aerosol in particles < 5.17 microns diameter. The Side-Stream nebuliser gave the best performance, although incorporation of a filter to trap exhaled antibiotic may prove difficult. The Micro-Cirrus generated a particularly fine aerosol. The Raindrop nebuliser performed well, while the Up-Draft II nebulised efficiently but was associated with extended nebulisation times which may limit its utility.