The aim of this study was to describe the technique of manual hyperinflation as applied by physiotherapists. Ten physiotherapists volunteered to manually hyperinflate a test lung. The protocol randomly altered resuscitation circuits (Laerdal and Macgill) and respiratory compliance conditions. Measurements of tidal volume, airway pressure, inspiratory flow rate and inflation rate were recorded during each test condition. The therapists applied a mean (SD) tidal volume of 1.4 (0.2) L with a mean (SD) airway pressure of 20.6 (6.6) cmH2O. The technique was significantly different between each test condition and between all therapists. Therapists were observed to hyperventilate the test lung and also apply positive end expiratory pressure with the Macgill circuit. A description of the technique on patients is required prior to evaluation of the technique in determining its effect on patients.