The immunopharmacological actions of nedocromil sodium are fully compatible with administration to man. Nedocromil sodium exhibits a wide range of anti-inflammatory actions. When compared with sodium cromoglycate, nedocromil sodium is more potent and a major difference is seen in the Ascaris-sensitised monkey subjected to bronchial challenge with specific antigen. In this model of chronic airway disease nedocromil sodium provides significant protection against changes in airway resistance and lung compliance provoked by antigen challenge. Sodium cromoglycate does not. This difference is most readily explicable by the greatly enhanced effect of nedocromil sodium, relative to that of sodium cromoglycate, in preventing the release of mediators such as histamine, leukotriene C4 and prostaglandin D2 from the cellular population of the chronically inflamed bronchus, especially from mast cells of the mucosal type. There is growing evidence that these mediators are important in allergic diseases of the eye and this additional activity may be expected to give nedocromil sodium extended scope in the management of conjunctivitis in which allergic inflammation and hyperresponsiveness are significant pathophysiological factors.