Ganciclovir and foscarnet are used for treatment of CMV retinitis, but cause hematologic toxicity and nephrotoxicity, respectively. Despite continued maintenance therapy with these drugs, relapse occurs in 85 percent of patients within 4 months. Studies suggest that MSL 109, a human monoclonal antibody, when given with either ganciclovir or foscarnet, may increase initial response and prolong time to progression in patients with CMV retinitis.