[AS PER AMENDMENT 1/7/98: Each subject receives sequential single doses of intravenous cidofovir, with a 2-week interval between doses and with concurrent probenecid. If the single doses prove safe and well tolerated and individual pharmacokinetic profiles are acceptable, subjects proceed to multi-dosing cidofovir given every 2 weeks for 6 months beginning 14-21 days after the second single dose. Subjects remain on intravenous or oral ganciclovir for treatment of CMV retinitis until they enter the multi-dosing phase of the study. Subjects who require reinduction during the multi-dosing phase receive intravenous cidofovir once weekly for 2 weeks before resuming the every-2-weeks regimen. Patients are stratified by age (3 months to < 2 years vs. 2 years to < 13 years), with 4 patients entered in the younger cohort and 8 in the older. In the younger age cohort, if 1 patient experiences life- or vision-threatening grade 3/4 toxicity or 2 experience non-life-threatening grade 3/4 toxicity, the age cohort will stop. If 1 patient experiences non-life-threatening grade 3/4 toxicity, 2 additional patients will be enrolled in this age cohort. In the older age cohort, if 1 patient experiences severe life- or vision-threatening toxicity or 2 experience serious, non-life-threatening toxicities, enrollment for both cohorts will be suspended while safety data are reviewed. If 2 of the 8 patients experience severe, non-life-threatening toxicity, enrollment may continue.]