Heparanase expression enhances both the number and size of tumor blood vessels. Seven weeks after subcutaneous injection of tumor cells, tissue sections from primary tumors were stained with antibody to CD34. Both vessel density (A) and the number of large microvessels (B) are significantly higher in tumors expressing high levels of heparanase (▪) as compared with controls (□). ^*P = .0009 for vessel density and P = .0005 for vessel size. Vessel size is plotted as the number of vessels per field greater than 0.1 μm². Error bars represent the mean plus or minus SD.