Human secreted proteins play a very important role in signal transduction. In order to study all potential secreted proteins identified from the human genome sequence, systematic production of large amounts of biologically active secreted proteins is a prerequisite. We selected 25 novel genes as a trial case for establishing a reliable expression system to produce active human secreted proteins in Escherichia coli. Expression of proteins with or without signal peptides was examined and compared in E. coli strains. The results indicated that deletion of signal peptides, to a certain extent, can improve the expression of these proteins and their solubilities. More importantly, under expression conditions Such as induction temperature, N-terminus fusion peptides need to be optimized in order to express adequate amounts of soluble proteins. These recombinant proteins were characterized as well-folded proteins. This system enables its to rapidly obtain soluble and highly purified human secreted proteins for further functional studies. (C) 2005 Elsevier Inc. All rights reserved.