Pegaptanib sodium injection (Macugen, Eyetech Pharmaceuticals, Pfizer, New York, NY, USA) is a relatively new medication intended to treat the so-called wet (neovascular ) form of age-related macular degeneration (AMD). This form of AMD is characterized by the growth of unwanted new blood vessels into the macula (angiogenesis). The aqueous solution containing pegaptanib is injected into the vitreous of the eye, where it binds to the 165 amino acid isoform of vascular endothelial growth factor (VEGF), a secreted protein that is thought to play a major role in the pathologic angiogenesis that occurs in wet AMD. Neovascular AMD is the leading cause of severe vision loss in people over age 60 in the United States and other industrialized countries (1). Pegaptanib acts as a selective VEGF antagonist through its molecular structure as an aptamer, a pegylated modified oligonucleotide that adopts a three-dimensional configuration, enabling it to bind to extracellular VEGF (Fig. 1). Aptamers are macromolecules composed of chemically synthesized single-stranded nucleic acids (either RNA or DNA) that bind with a high degree of selectivity and affinity when exposed to target proteins. Pegaptanib binds VEGF165, and bound VEGF165 is not able to bind to the VEGF receptor, thereby negating its ability to cause angiogenesis and vascular permeability. Other aptamers exist, as do other forms of treatment for AMD. To date, however, no treatment for AMD has allowed for better vision after treatment, with most surgical treatments leading to almost immediate loss of some vision in the expectation of preventing more severe loss. Research in the field of macular degeneration is advancing rapidly, and treatment with an aptamer such as pegaptanib is a viable option despite the possibility of adverse events.