After 2 weeks of observation, Nedocromil has been studied in double blind vs placebo for 8 weeks in 40 children with asthma of medium seriousness. Patients had to record on a clinical diary symptoms (wheezing and cough), beta 2-agonists consumption and collateral effects of the drug. Every 2 weeks patients had a clinical examination and the physician's judgement about the treatment's efficiency was registered. Patients who took the active drug had an improvement in symptoms from the 3rd week of observation and a significative decrease in bronchodilators' consumption. The judgement about the treatment's efficiency was different between physician and patients thus preventing the recognition of the patients who had taken Nedocromil from those who had taken placebo. We think that the different consumption of beta 2-agonists could be the reason for this behaviour between the 2 groups.