The latest “trend” in oligonucleotide therapeutics is the development of therapeutic siRNA molecules. As its name suggests, RNA interference (RNAi) is a cellular mechanism regulating the expression of genes and also the replication of viruses. The mechanism is mediated by double-stranded small interfering RNA molecules (siRNA). Discovered in 1998, siRNA is the latest biotechnology breakthrough that raises hopes for discovery of the “magic bullet” that would allow the specific targeting of any disease-relevant gene. In theory, siRNA therapeutics can be 100% specific for a particular gene, because the sequences can be selected to interact with one particular mRNA only. Only 6 years after discovery of the therapeutic opportunities in siRNA molecules, two companies, Sirna and Acuity Pharmaceuticals, have already entered clinical trials with siRNA compounds targeted against vascular endothelial growth factor (VEGF) for treatment of age-related macular degeneration (AMD).