In order to evaluate the efficacy and tolerability of lodoxamide in the treatment of allergic conjunctivitis, the authors conducted a double-blind trial with intrapatient comparison on 32 patients, using lodoxamide versus spaglumic acid in the course of two conjunctival provocation tests performed with specific allergens. The patients received one drop of lodoxamide in one eye and one drop of spaglumic acid in the other; 15 minutes later, 25 microliters of allergen extract at a pre-established concentration was instilled. After 10 minutes, the signs and symptoms of the allergic response were evaluated and recorded. Six hours later, the instillation of the allergen extract in both eyes was repeated following the same procedure, to establish the duration of the effect of the two drugs. The results, obtained by evaluating the main clinical signs and symptoms (itching, lacrimation, hyperaemia, palpebral oedema and chemosis), demonstrate with statistically significant differences that lodoxamide inhibits the conjunctival response to exposure to the allergen with greater efficacy than spaglumic acid, and for a longer duration. The two drugs provided similar and satisfactory tolerability. In view of these results, lodoxamide can definitely be considered and effective drug in the treatment of allergic conjunctivitis.