RNA interference using small interfering RNAs which target HIF-1 alpha mRNA inhibit expression of the HIF-1 alpha gene. As HIF-1 alpha is a transcriptional regulator of VEGF, expression of VEGF is also inhibited. Control of VEGF production through siRNA-mediated down-regulation of HIF-1 alpha can be used to inhibit angiogenesis, in particularly in diseases such as diabetic retinopathy, age related macular degeneration and many types of cancer.