Two forms of heat-stable, zinc-containing beta-lactamase II have been described for strains of Bacillus cereus and have been shown to differ in substrate specificity (R. B. Davies, E. P. Abraham, J. Fleming, and M. R. Pollock, Biochem. J. 145: 409-411, 1975). We report here the nucleotide sequence, inferred amino acid sequence, and expression of beta-lactamase II from B. cereus 5/B/6 and compare our results with those for its homolog characterized in B. cereus 569/H (M. Hussain, C. Anthony, M. J. Madonna, and J. O. Lampen, J. Bacteriol. 164: 223-229, 1985) to document amino acid differences contributing to the specific properties of these enzymes.