The human interferon alpha 2b (hu-IFN alpha 2b) gene was cloned in Escherichia coli JM109(DE3) and the recombinant protein was expressed as cytoplasmic inclusion bodies (IB). The present work discusses the recovery of hu-IFN alpha 2b IB from the E. coli cells. An optimized protocol is proposed based on the sequential evaluation of recovery steps and parameters: (i) cell disruption, (ii) IB recovery and separation from cell debris, (iii) IB washing, and (iv) IB solubilization. Parameters such as hu-IFN alpha 2b purity and recovery yield were measured after each step. The optimized recovery protocol yielded 60% of hu-IFN alpha 2b with a purity of up to 80%. The protein was renatured at high concentration after recovery and it was found to display biological activity. (C) 2005 Elsevier Inc. All rights reserved.