In a prospective, randomized study we examined the effect of (i) ambulatory oxygen and (ii) a portable, inspiratory pressure support (IPS) device on the endurance shuttle walk test (ESWT) in patients with severe chronic obstructive pulmonary disease (COPD). Ten outpatients [median (range) FEV1 0.60 l(0.35, 1.45)] performed the ESWT under five test conditions: baseline walk (no assistance), IPS at 14 cmH2O from a portable ventilator (the HIPPY, Friday Medical, U.K.), sham IPS (< 8 cmH2O), ambulatory oxygen at 2 l min(-1), and sham oxygen (carrying the portable oxygen cylinder and breathing air). There were significant improvements in the ESWT with ambulatory oxygen, but a negative effect with the HIPPY device [mean (SD) time: baseline 172 (48) sec; oxygen 242 (62) sec; HIPPY 84 (35) sec]. The ESWT appeared sensitive to the effect of cylinder weight although differences in endurance capacity were not significant [sham oxygen 151 (45) sec]. The ESWT was sensitive to the acute application of oxygen, demonstrating a beneficial effect on endurance performance in patients with severe COPD. The ESWT could form the basis of a standardized assessment for ambulatory oxygen.