The purpose of this prospective randomised cross-over study was to measure peak expiratory flow rates during manual hyperinflation and to determine if the addition of a head-down tilt to physiotherapy treatment increased sputum production in patients who are intubated and ventilated. Twenty patients who were intubated, ventilated and haemodynamically stable were randomised to a sequence of physiotherapy treatment in a flat side-lying or a head-down tilt position. Peak expiratory flow rates were measured for each breath during manual hyperinflation using a Vitalograph peak flow meter. Sputum wet weight was collected for each treatment position and static pulmonary compliance was measured before and immediately following physiotherapy treatment. There was a significant increase in peak expiratory flow (p < 0.001) and sputum production (p = 0.008) in the head-down tilt position. The mean difference and 95% confidence intervals for expiratory flow were 0.17 (0.15 to 0.19) l/sec and for the wet weight of sputum 1.97 (0.84 to 3.10) g. The peak expiratory flow rate was sufficient to produce annular flow in both flat side-lying (1.97 +/- 0.09) l/sec and in the head-down tilt position (2.14 +/- 0.08) l/sec. Static pulmonary compliance improved significantly following physiotherapy treatment (p = 0.003). The mean difference and 95% confidence intervals pre- and post-treatment for static pulmonary compliance were 5.18 (2.14 to 8.22) ml/cmH(2)O. The results suggest that addition of a head-down tilt to physiotherapy treatment, including manual hyperinflation, in patients who are intubated and ventilated, increases sputum production and improves peak expiratory flow.