Spacer devices are important aids for use with metered dose inhalers in children with asthma. However, expense and unavailability of commercially produced spacers in developing countries have limited their use. Home-made spacers in the form of cups or bottles are widely used despite a lack of data confirming their efficacy. We investigated the relative efficacy of three spacers (a commercially available spacer, a modified 500-ml cold drink bottle and a polystyrene cup) for delivery of aerosolized drugs to asthmatic children older than 5 years. We also investigated the effect of leaks in the delivery system by comparing delivery via a sealed and an unsealed cold drink bottle. Lung deposition of aerosolized Tc-99m DTPA inhaled via spacer was measured in 30 patients. The median aerosol deposition in the lungs was significantly greater for the conventional spacer than for the cup (31.5% vs 9.5%; Z = -2.8, p = 0.005). Median aerosol deposition for the conventional spacer and sealed bottle were equivalent (40.5% vs 44%). Aerosol deposition from the sealed and unsealed bottle was significantly different (43.5% vs 24%; Z = -2.54, p = 0.01); however, the unsealed bottle was more efficient than the cup. We conclude that a modified 500-ml cold drink bottle is an efficient spacer. Leaks in this system are a major factor affecting the amount of drug deposited. The modified polystyrene cup is not an efficient spacer, delivering between a third and a fifth of the dose that other spacers were capable of delivering.