Recent reports have suggested a role for BW-B759U in the treatment of cytomegalovirus retinitis. The present study presents the ophthalmoscopic features in three treated patients, and examines the microscopic findings in the eyes of the first patient ever treated with BW-B759U for cytomegalovirus retinitis. Ophthalmoscopic findings of improvement on drug therapy included remission of perivascular infiltration, stabilization of the extent of the retinal area involved, and development of a pigmented chorioretinal scar in the involved area. Relapses occurred with cessation of therapy, and repeated courses of therapy were required. One patient developed a rhegmatogenous detachment with retinal breaks in an atrophic area of treated retinitis. Electron microscopic examination of the eyes of one patient disclosed the persistence of cytomegalovirus inclusions in retinal cells despite previous drug therapy. These findings suggest a virostatic action for BW-B759U.