A 31-year-old homosexual man with AIDS, bilateral cytomegalovirus (CMV) retinitis and optic neuritis in one eye, was treated with DHPG. The drug is an acyclic nucleoside analogue of guanosine with antiviral activity. The visual acuity at the start of treatment was R.E.: no light perception and L.E.: 1.25. There was bilateral regression of retinal exudates on DHPG 5 mg/kg twice a day during 2 weeks. The visual result however was poor because of the optic nerve involvement, which did not improve during DHPG treatment. Four weeks later there was a recurrence of retinitis with the development of exudative retinal detachment in the eye with optic neuritis, despite maintenance therapy of 5 mg/kg once a day Monday through Friday. The dose was increased to 5 mg/kg twice a day, but after 1 week treatment had to be discontinued because of neutropenia. Eight days later treatment was restarted with DHPG 5 mg/kg in a single daily dose during 17 days, which led to remission of retinitis but retinal reattachment did not occur. Thereafter maintenance therapy was continued. Visual acuity remained unchanged. DHPG appears to be effective in treating cytomegalovirus retinitis but long-term suppressive therapy would be necessary to prevent recurrence of the retinitis.