The recombinant plasmids harboring a heterologous gene coding mouse endostatin were transfected and expressed stably in Drosophila melanogaster S2 cells. Recombinant endostatin expressed in the stably transformed S2 cells was secreted into the medium. Recombinant endostatin was also purified to homogeneity using a simple one-step Ni2+ affinity fractionation method. The purification yield was approximately 4 mu g from the medium fraction of 8 ml cultures of stably transformed S2 cells. In a T-flask, the stably transformed S2 cells produced 24 mg recombinant endostatin/l at 7 days post-induction by 0.5 mM CuSO4. In a high aspect rotating-wall vessel designed by NASA to simulate microgravity, the S2 cells produced up to 13 mg recombinant endostatin/l.