Eleven patients with leukemia refractory to conventional therapy were treated with high doses of cytarabine (3 g/m2 intravenously every 12 hours for six days) followed by daunorubicin (30 mg/m2/day intravenously for three days). Each patient received, in a double-masked, randomized manner, either 1% prednisolone phosphate or placebo eyedrops in each eye 12 hours before and along with the cytarabine so that we could determine whether a topical corticosteroid prevents corneal toxicity from systemic cytarabine. Ten of the 11 patients had a significant reduction in the intensity and duration of the symptoms and signs of corneal toxicity in the corticosteroid-treated eye (P less than .0005). In the placebo-treated eye, pain, photophobia, and tearing occurred at a median time of 6.5 days after initiation of therapy but resolved in approximately one week. Patients receiving high doses of intravenously administered cytarabine should receive topical corticosteroid prophylaxis to reduce the corneal toxicity associated with this treatment.