There have been few works studying the effects of training in asthmatics and there does not yet exist any study utilising the idea of the individualization of training. This is why the aim of this study was to assess the value of the effects of individualised aerobic training on cardio-respiratory aptitude in the asthmatic child. This study was carried out on two populations of asthmatics, swimmers and non-swimmers matched for age, height, degree of bronchial obstruction during a remission and baseline of physical fitness. Each child in the swimming group was trained to a metabolic level corresponding to the ventilatory threshold. After a period of 3 months a second cardio-respiratory evaluation was carried out. A clear cut improvement (20%) of VO2 max was observed as well as a proportional elevation of the ventilatory threshold in the swimming group. The VE max, the VT max, the VT/Timax, the FC max and the maximal oxygen uptake were also recorded. On the other hand aerobic training seems to be without effect on resting pulmonary function, even if the clinical state of the children improved. In conclusion this study shows that aerobic training closely adapted to the level of each child, obtains an important and rapid gain in cardio-respiratory fitness which leads to a better exercise adaptation. In addition the progression of the ventilatory threshold implies an increased capacity for work without the appearance of hyperventilation. This enables an understanding of how aerobic training is generally accompanied in the asthmatic with a better respiratory comfort and argues in favour of the perfect efficacy of this type of reconditioning in the re-adaptation to effort in these patients.