AMENDED: The ACTG 093 optional extended maintenance therapy period will conclude on January 2, 1991 in order to facilitate timely analysis of this study. All patients who wish to continue foscarnet therapy should be referred to Astra Protocol 90-FOS-14 at telephone number 800-292-5775. Original design: Patients are placed into two groups: (1) patients who have a sight-threatening lesion in the retina of an eye with vision that can be saved (corrected vision of 20/100 or better) and who cannot be treated with DHPG, and (2) patients whose retinitis has quickly gotten worse and/or has shown resistance to DHPG treatment. Both groups will receive a beginning (induction) dose of foscarnet by vein (IV) for 2 weeks, followed by a maintenance dose for 8 weeks with an option to continue up to 24 weeks. AMENDED: Patients entering the study on or after 01/02/90 receive the standard two week course of foscarnet induction therapy and receive maintenance therapy. Treatment is given for a ten week study period or until progression occurs or toxicity endpoints are reached. If retinitis is stable and foscarnet well-tolerated, maintenance therapy may be extended for a period not to exceed 1 year.