Superoxide dismutase (SOD)-deficient Escherichia coli OX326Acells are protected against chemically-induced oxidative stress by expression of the chaperonin GroESL. This protection is equivalent to expression of superoxide dismutase even though GroESL has no inherent SOD activity. Co-overexpression of GroESL and SOD in the same cells results in higher protein yields of SOD and greater metallation of SOD when compared with expression of SOD alone. Greater metallation results in the higher specific activity of SOD that is observed in heat shock, and is not due to increased synthesis of SOD mRNA or protein.