Following routine evaluation studies, patients are randomized to receive foscarnet right away or to delay treatment, as their retinitis has been determined not to be immediately sight-threatening. Patients are hospitalized for the first 3 days and may remain hospitalized for as many as 14 days. Foscarnet is given by vein (IV) in what is called induction therapy, and if the patient's retinitis stabilizes after 2 weeks of treatment, treatment with foscarnet is continued in maintenance therapy for another 8 weeks. During maintenance therapy, patients receive salt solution IV to help prevent any toxic side effect of foscarnet on the kidneys. Patients have regular checkups to monitor their retinitis as well as their general health. Patients taking zidovudine (AZT) prior to entering the study may continue their treatment if they are selected for the delayed treatment group; if they are selected for the immediate treatment group, they begin or resume AZT therapy when they enter the 2nd week of maintenance therapy. Patients are followed as outpatients for at least 10 weeks, with clinic check-ups and lab tests once every week; eye exams are done once a week for the first 2 weeks and then every other week. If clinically indicated, a continued maintenance regimen may be administered after the 10th week; the total duration of therapy plus maintenance is not to exceed 24 weeks. Note: Patients scheduled for the delayed foscarnet treatment are immediately given foscarnet at the first sign that their retinitis is getting worse.