The effect of two types of physical training on patients with perennial asthma were compared in a blind, controlled, randomized study. Eleven of 27 adults with asthma performed a physical training programme which did not change their oxygen consumption (control group). The remaining 16 asthmatics performed a physical training programme which improved their maximal oxygen consumption (training group). Both of the training programmes were performed for 1 hour, twice a week during a period of 2 months. No complications were reported during the performance of the training programmes. The doses of all medicines apart from beta 2-agonist aerosol were unchanged during the training period. The patients inhaled beta 2-agonist aerosol if their peak expiratory flow (PEF) was less than 60% of their maximal PEF. The training group decreased their use of aerosol from an average of 4.94 puffs per day to 3.41 puffs per day (P less than 0.05). The control group did not change their use of beta 2-agonist aerosol significantly. It is concluded that physical exercise which improves the maximal oxygen consumption decreases the use of beta 2-agonist spray and that heavy exercise is well tolerated by asthmatics.