Human erythropoietin (HuEPO) gene was inserted into an SV40-based episomal vector with a temperature-sensitive large T antigen which enabled uncontrolled plasmid replication and inducible HuEPO production at temperatures below 33 degrees C. Good productivity of HuEPO was obtained when temperature was lowered to 30 degrees C at relatively higher cell density in Petri dish culture. Therefore, we cultured the cells immobilized on microcarriers in a spinner flask at 37 degrees C until the cell density reached 1.8 x 10(4) cells/cm(2)-microcarrier surface area, and then the temperature was lowered to 30 degrees C for HuEPO production. Using this process, HuEPO productivity was enhanced 7-18 times that of the Petri dish cultures, and a high concentration of HuEPO was accumulated in the medium.