Forty eight eyes of 42 patients with choroidal neovascular membranes and age-related macular degeneration who received three different dose regimens of systemic interferon alfa-2 were studied retrospectively. The response to treatment of 41 eyes of the 37 patients who received at least 4 weeks' treatment was analysed with respect to the change in size of the choroidal neovascular membrane and the visual acuity compared with pretreatment levels. The size of the membrane at the end of the course of treatment had decreased in seven (17%) eyes overall, not changed in 16 (39%), and increased in 18 (44%). At the end of treatment, the visual acuity had improved in seven (17%) eyes, not changed in 27 (66%), and deteriorated in seven (17%). With an average follow up of 10 months after treatment, the visual acuity had deteriorated compared with the pretreatment value in 21 out of 41 (51%) eyes. Vision improved in some fellow eyes with disciform scars. Side effects were common and often severe. The data suggest that one of the major effects of interferon alfa may be to decrease vascular permeability. While further research may identify a place for interferon alfa in the treatment of choroidal neovascularisation, we were unable to demonstrate that the treatment regimens of systemic interferon alfa we used caused a dramatic benefit to patients with exudative age-related macular degeneration.