In vitro data suggest that combination therapies are synergistic in inhibiting viral replication; these therapies include a foscarnet-ganciclovir combination and a cidofovir-ganciclovir combination. In the SOCA--CMV Retinitis Retreatment Trial, the combination of intravenous ganciclovir and foscarnet was more effective than either drug alone for the treatment of relapsed retinitis. Therefore, the combination of intermittent intravenous cidofovir and daily oral ganciclovir may be an attractive therapy for relapsed disease because it may provide synergy for controlling both ocular and visceral disease while not necessitating either a central venous catheter or an intraocular surgical procedure.