• Fluorouracil is given for a variety of neoplasms by various administrative routes. Toxicity of susceptible normal tissue limits systemic dosage, but at this level intraocular tissue may not receive tumor-inhibiting concentrations. Subconjunctival administration of 6.25 mg of 14C-fluorouracil in 0.5-mL dosages resulted in a peak anterior chamber concentration of 69.5 μg/mL and a peak vitreous concentration of 10.5 μg/mL over the 12 hours tested. This resulted in no visible ocular damage. The intraocular levels achieved were greater than the concentration reported to inhibit selected tumors. The total dosage administered was considerably below the level of systemic toxicity.