Sodium cromoglycate stabilizes mast cell membranes and prevents the release of histamine and other biochemical mediators. When topically applied to the eye before allergen exposure, ocular sodium cromoglycate prevents many of the signs and symptoms associated with type I allergic reactions (which includes hayfever, acute allergic and chronic allergic conjunctivitis, and vernal keratoconjunctivitis) and giant papillary conjunctivitis. Although difficulties exist in evaluating clinical trials in allergic eye disease, both open and controlled studies have shown ocular sodium cromoglycate to be very effective in relieving the subjective symptoms and clinical signs of the above ocular disorders. In addition, ocular sodium cromoglycate may decrease the need for supplementary oral antihistamines and, more importantly, the need for ocular corticosteroids, thus decreasing the incidence of steroid-induced ocular side effects. However, in severe cases and in instances of acute exacerbation of symptoms, the combined ocular application of sodium cromoglycate and corticosteroids may be very effective. No systemic or severe adverse reactions have been attributed to ocular sodium cromoglycate, which is not surprising since systemic drug absorption from the eye is minimal. However, transient local stinging and burning have been reported. Thus, although further studies in giant papillary conjunctivitis and comparative studies with corticosteroids in allergic conjunctivitis and vernal keratoconjunctivitis are needed to more clearly define the extent of benefits that may be obtained from ocular sodium cromoglycate, it is clear that the safety and efficacy of the drug in type I allergic eye diseases is such that it should be considered as a first-line agent when drug therapy of these disorders is indicated.