A highly efficient Escherichia coli-based, batch in vitro protein synthesis system using circular plasmid DNA is described. Compared to a presently available commercial kit, this improved system produced several hundredfold greater yields of the rDNA human protein thrombopoietin (ca. 450 micrograms/mL). The system is capable of obtaining specific synthesis rates similar to those in vivo, approximately a 1000-fold increase compared to the original methods previously described. It compares favorably in rates and yields to the recently published semicontinuous methods but with the convenience of a true batch system.