Nedocromil sodium, a non-toxic pyranoquinoline dicarboxylate, was developed as a novel topical treatment for allergic inflammatory lung diseases. With a broader pharmacological potential than the chromone compound sodium cromoglycate, nedocromil sodium has more potent antiinflammatory effects whilst maintaining a good safety profile due to rapid excretion, unmetabolized. Having the ability to stabilize both mucosal (MC(T)) and connective tissue (MC(TC)) mast cells and directly to inhibit activated cells such as eosinophils, which are involved in continuing allergic inflammation in the eye as well as in the airways, nedocromil sodium appears ideally suited to the treatment of allergic conjunctivitis. Preliminary therapeutic trials have confirmed efficacy and the lack of side-effects of the 2% eye drop formulation of nedocromil sodium, and its comparative potency which permits twice-daily administration for seasonal ocular symptoms, with the safe option of increasing to four times daily use for more severe, chronic allergic inflammatory conditions. With many patients already symptomatic at the start of trial treatment, nedocromil sodium eye drops have also proved to have a rapid onset of action providing relief of symptoms in 24 hours in the majority of cases, and often within one hour of the first dose.