I discussed following four points. 1. Weaning means an increase in energy demand. For successful weaning, stable hemodynamics and good nutrition are mandatory. 2. Success or failure is closely related with the "reserve" factors of the patients, including those discussed in 1. These "reserve" factors may be difficult to evaluate from the spirometry/pulmonary function data only. 3. A dissociative movement between chest wall and abdomen indicates that the weaning is likely to fail. The data, however, are inconclusive. 4. Few occasional patients are successfully weaned by the classical on-off method, after failing to be weaned by the standard IMV. We interpret that the classical on-off method has more elements of training. This point should be taken into consideration and this aspect of training should be pursued for weaning.