Previous studies have reported that exercise tolerance improves with transtracheal oxygen delivery. However, patients were not blinded to the delivery technique used, introducing a potential source of bias. The purpose of this study was to compare exercise tolerance during nasal cannula and transtracheal delivery using a randomized double-blinded technique. Subjects (n = 11) performed 12-min walks on the same day while receiving nasal cannula and transtracheal delivery. Nine of 11 subjects walked farther with transtracheal delivery, a significant increase (p less than 0.01). Mean increase in walk distance was 95 +/- 86 feet. In addition, a trend was seen toward greater improvement in walk distance with greater flows through the catheter (r = 0.58, p less than 0.06). Time into the walk when desaturation (SaO2 less than 90%) first occurred was not significantly different. We conclude that exercise tolerance improves when oxygen is delivered by transtracheal catheter. This improvement is unrelated to an increase in SaO2. We speculate that the increase in exercise tolerance may be related to other physiologic effects of flow through the catheter.