SummaryA controlled clinical trial comparing inhalation of disodium cromoglycate (DSCG) and of ICI 74,917 was carried out using a double‐placebo technique in thirty‐two patients with extrinsic asthma already shown to be reasonably responsive to DSCG. In view of the fact that ICI 74,917 is 300 times more potent than DSCG in inhibiting antigenic challenge in animals a better effect was anticipated from the new drug in the human asthmatic subject. Whilst this was not obtained, there appeared to be no lesser effect than that of D