In prostate cancer PC-3 xenografts-bearing mice, VEGF siRNA-PEG/PEI polyelectrolyte complex markedly downregulated VEGF gene expression at both the transcriptional and protein levels in the tumor, leading to reduced tumor microvessel density and the most potent tumor growth suppression compared to the naked siRNA and siRNA/PEI complex. The gene discussed is VEGFA; the disease is prostate carcinoma.