Described are some pharmacokinetic parameters for 5-fluorouridine, a potentially useful intermediate metabolite of 5-fluorouracil (5-FU), following subconjunctival and intravitreal injection in the pigmented rabbit. Immediately following a 500 microgram intravitreal injection of 3H-5-fluorouridine, a peak ipsilateral vitreous concentration of 308 micrograms/ml was measured. This decreased to 199 micrograms/ml at 2 hours, 33 micrograms/ml at 12 hours and 4.4 micrograms/ml at 24 hours, indicating that 5-fluorouridine is cleared from the vitreous at a rate similar to 5-fluorouracil. Aqueous concentrations in the ipsilateral eye reached a maximum at 6 hours (9.6 micrograms/ml) and decreased to 0.8 micrograms/ml at 24 hours. Following subconjunctival injection of 5 mg 3H-5-fluorouridine (0.5 ml), peak ipsilateral anterior chamber concentration of 10.7 micrograms/ml was measured 1 hour after injection and decreased to 2.4 micrograms/ml after 12 hours. Maximum vitreal concentrations of 1.7 micrograms/ml were measured 12 hours after injection.