Fomivirsen, a novel treatment for sight-threatening cytomegalovirus (CMV) retinitis, is on track to become the first antisense agent to make it to the clinic. Infection with CMV, a herpesvirus, is generally asymptomatic in immunocompetent individuals. However, CMV retinitis is among the most common opportunistic infections seen in patients with HIV infection. It typically occurs late in the disease and can cause blindness. Researchers reported favourable results with fomivirsen [Isis Pharmaceuticals] in a phase III clinical trial in patients with advanced, refractory CMV retinitis, at the 11th Conference of the International Society for Antiviral Research [San Diego, US; April 1998].