Patients are randomly placed in one of two treatment groups. In one group, patients receive DHPG twice a day, intravenously, for 14 days, followed by a daily dose for 14 weeks. Patients in the other group (the delayed-treatment group) do not receive immediate treatment with DHPG. Patients in both groups have regular ophthalmologic (eye) evaluations with retinal photographs to see if the retinitis is getting worse. Patients in the delayed treatment group receive DHPG if this occurs.