To determine the dose of inhaled budesonide suspension in the treatment of preterm infants with ventilator-dependent lung disease, we measured the dose of nebulized budesonide delivered through an endotracheal tube (ETT), using a test lung and filters. The effect of delivering the nebulized aerosol to two different locations in the same ventilatory circuit was evaluated. In addition, a new synchronized jet nebulizer was tested. The median drug delivery to the test lung was 0.3% (range, 0-0.4%) of the nominal dose when the nebulizer activated by continuous gas flow was inserted into the inspiratory line of the circuit. Drug delivery could be increased to 0.7% (range, 0.5-0.8%) by delivering the nebulizer output directly to the ETT. When using the synchronized jet nebulizer, drug delivery was 1.1% (range, 0.8-1.6%). The particle size of aerosol emerging from the ETT was 2.14 microns. The nebulization time with the synchronized nebulizer set-up was 38 min, while the other set-ups delivered an equal volume of solution in 6-7 min. Drug delivery of 0.3-1.1% to the test lung illustrates the problems encountered in aerosol treatment of intubated neonates. We conclude that the delivery of budesonide to the test lung can be increased by delivering the nebulizer output to the ETT directly. Using synchronized nebulization during inspiration only can achieve further increases in drug delivery, and wastage of drug during expiration is decreased. Synchronized nebulization may, therefore, have an important place in the delivery of expensive aerosolized drugs.