Sodium fluorescein solutions, 3 ml of 25% solution and 5 ml of 10% solution, were compared with a double-blind crossover method in a group of 41 normal volunteers and in a group of 42 patients who had diverse ophthalmic disorders. Following injection of the solutions into the antecubital vein, visualization, serial fluorescein angiograms, and five-minute phase angiograms were studied and compared. The untoward reactions reported in both studies were of types usually associated with sodium fluorescein, the most common of which was a mild, transient nausea. On the basis of our results, there is no significant difference in the incidence and severity of adverse reactions between the 10% and 25% solutions. In the volunteer study, the 25% solution was significantly superior in visualization and paired comparison (P less than .001) in the patient study, the 25% solution was significantly superior in angiogram quality (P less than .01), five-minute phase angiogram (P less than .05), and paired comparison (P less than .005). The overall superiority of the 25% concentration in a 3-ml volume was demonstrated both subjectively and objectively in the volunteer study and in the patient study.