Recombinant tumstatin was expressed in stably transformed Drosophila melanogaster S2 cells and secreted into the medium with a molecular size of 29 kDa. Recombinant endostatin was also purified to homogeneity using a simple one-step Ni2+ affinity fractionation. Purified recombinant tumstatin inhibited endothelial cell proliferation in a dose-dependent manner. The concentration at half-maximum inhibition for recombinant tumstatin was approx. 0.7 g ml(-1). A maximum production of 4.6 mug recombinant tumstatin (10(7) cells)(-1) was obtained in a T-flask culture of S2 cells, 7 d after induction with 0.5 mM CuSO4.