In a study in double-blind it has considered if the procaterol, given for a month, had been able to develop a preventive action in children affected from relapsing asthmatic bronchitis. For that the clinical symptomatology, the number of the contagious events and the consumption of the drugs have been valued for two following months. The patients who had taken the procaterol, presented a reduction of the contagious events, of the consumption of the drugs and of the spastic bronchus symptomatology in the first month of the treatment which continued in the second month. In spite of the development of the contagious events, in the third month, the pulmonary symptomatology resulted inferior in comparison with the group of check. It is likely than the treatment with procaterol avoids the arisen of the spastic-bronchus symptomatology for a rise of the threshold of bronchial re-established, consequent to the re-establishment of the mucous lesions.