A formulation containing recombinant endostatin attached to polyethylene glycol (PEG), with potential anti-angiogenic and antineoplastic activities. Endostatin, a 20 kDa C-terminal proteolytic fragment of collagen XVIII, induces microvascular endothelial cell apoptosis and inhibits endothelial proliferation and angiogenesis, which may result in a reduction of tumor cell growth. Modification with PEG extends the circulation half-life of endostatin, improves stability and increases solubility in organic solvents. Check for active clinical trialsusing this agent.