No / Lung inflation is the most important, and most difficult step in newborn resuscitation. A wide variety of devices are used to achieve lung inflation, but there are relatively few data to guide clinicians in their choice of device. We tested the ability of instructors and trained candidates on a newborn life support course to deliver initial inflation breaths to a test lung, using a pressure limited blow-off valve, a 240-ml self-inflating bag and a 500-ml self-inflating bag in sequence. Use of a 240-ml self-inflating bag was associated with shorter initial inflations of 1.8 s mean (95% CI 1.60-1.99 s), compared with 2.42 s (2.24-2.61 s), 2.40 s (2.08-2.71 s) for 500-ml self-inflating bags and 'Tom Thumb' T piece, respectively. Delivery of breaths within a target pressure range of 30 � 5 cm H2O was significantly better using a T piece than either self-inflating bag (proportion within target range 0.05 (95% CI 0-0.11), 0.17 (95% CI 0.12-0.23), 0.89 (95% CI 0.83-0.94) for 240-ml and 500-ml self-inflating bags and 'Tom Thumb' T piece, respectively. Excessive pressure delivery with both sizes of self-inflating bag was frequent. These data do not support use of 240-ml or 500-ml self-inflating bags for resuscitation of newborn term infants. A variable pressure T piece blow-off system may be the easiest device to use for newborn resuscitation and the most reliable at delivering desired pressures for set times.