OBJECTIVE: The objective of this study was to explore preweaning mood state and dyspnea, in mechanically ventilated patients. METHODS: Before ventilatory weaning, 21 critically ill patients completed the short profile of mood states (higher scores equal greater disturbance), and a 10 cm dyspnea visual analogue scale (none to extremely severe). Weaning outcome at 24 hours was recorded. RESULTS: The mean +/- SD total mood disturbance (possible range, 0 to 16) and subscale scores (possible range, 0 to 4) were as follows: total, 6.10 +/- 4.06; tension, 1.07 +/- 0.64; depression, 1.16 +/- 0.93; anger, 1.05 +/- 0.82; vigor, 1.04 +/- 0.84; fatigue, 1.96 +/- 0.90; and confusion, 1.27 +/- 0.91. Mean dyspnea was 3.22 +/- 2.26 cm. Dyspnea intensify correlated negatively with vigor (r = -0.38, P <.10). Lower preweaning vigor tended to differentiate successful from unsuccessful weaning (Mann-Whitney U = 22.0; P=.07). CONCLUSION: Patients who weaned successfully experienced greater mood disturbance. Moderate mood disturbance may be a necessary stimulus for successful weaning.