The effect of oxygen, paraquat (PQ2+; 1,1′-dimethyl-4,4′-bipyridinium dichloride) and 2,2′-dipyridyl (2,2′-DP) on the synthesis of superoxide dismutase (SOD) in various microorganisms was examined to determine whether the control of SOD biosynthesis in other prokaryotes is similar to that in Escherichia coli. All of the strains tested, with the exception of Alcaligenes faecalis, exhibited SOD levels proportional to the concentration of oxygen in the growth media. Paraquat induced SOD in all of the strains surveyed except Staphylococcus epidermidis, Streptococcus faecalis, and Listeria monocytogenes. The iron chelator, 2,2′-DP, induced SOD in Proteus vulgaris, Enterobacter cloacae and Staphylococcus aureus, but decreased the activity of SOD in A. faecalis and Pseudomonas aeruginosa and had no effect in S. epidermidis, S. faecalis or L. monocytogenes. The data indicate that the induction of SOD in P. vulgaris, E. cloacae, and Salmonella typhimurium is similar to that found in E. coli and suggest that the mechanism of SOD regulation in E. coli may be representative of the Enterobacteriaceae family as a whole.