We present a case of cytomegalovirus (CMV) retinitis in an AIDS patient who survived for 10 months after the start of his ocular problems. The retinitis responded to dihydroxy propoxy methyl guanine (DHPG) but relapsed four to six weeks after each course of treatment with progressive retinal destruction. One relapse was therefore treated with trisodium phosphoformate hexahydrate (Foscarnet). There are few reports of the use of this drug in the treatment of CMV retinitis with AIDS, but it appeared to be less effective in our patient than DHPG, possibly because of poor penetration of the blood-ocular barrier. A final course of outpatient maintenance therapy with DHPG failed to prevent a preterminal relapse of the retinitis. Fundus photographs demonstrated the resolution and relapse of the retinitis associated with each course of treatment. Maintenance therapy with DHPG would appear to be necessary to prevent relapse, but the logistics of this are difficult, and the effective dosage of DHPG is as yet uncertain.