The practicality of long term patient triggered ventilation using airflow changes was assessed in 22 infants with a median gestational age of 29 weeks (range 25-33 weeks). Inflation time during patient triggered ventilation was limited to 0.4 seconds or less. Initially it was associated with improvements in oxygenation in most infants. Patient triggered ventilation was maintained till final extubation in 13 of the infants without complications. Only one infant developed a pneumothorax, but in the remaining eight infants (who tended to be less mature (p less than 0.01) it had to be discontinued after only a few hours. Predictors of failure of patient triggered ventilation at one hour were both a lack of improvement in oxygenation, and a relatively slow triggering rate that was related to gestational age. We conclude that long term patient triggered ventilation is practical for preterm neonates, but only for those more mature than 28 weeks' gestational age.