In Stage 1, up to 30 patients are randomized to either observation with deferral of treatment until the retinitis progresses (observation group), or to intravenous HPMPC at the higher dose for two consecutive weekly induction doses, followed by the lower dose every other week for maintenance. In Stage 2, up to 70 patients are randomized to observation or to HPMPC at the higher dose for two consecutive weekly induction doses followed by either dose every other week for maintenance, for a total of three treatment groups. Concomitant saline hydration and probenecid are administered to patients receiving HPMPC.