The IC50s of GD-40 were comparable to those of earlier β-lactamase inhibitors (clavulanic acid and sulbactam) and higher than those of more recently introduced compounds (tazobactam and brobactam) against TEM-1 and SHV-2 β-lactamases obtained from Escherichia coli strains.Thus, GD-40 and other 6α-halo-2β-chloromethylsulfones may be of value as inhibitors of both broad- and extended-spectrum β-lactamases.