A series of 2 beta-[(4-substituted)-1,2,3-triazol-1-yl]methyl penicillanic acid sulfones was synthesized as P-lactamase inhibitors. Many of these compounds showed good in vitro inhibitory activity against penicillinase, cefotaximase and plasmid-mediated class III TEM enzymes, but exhibited weaker cephalosporinase inhibition. One member in this series-2 beta-[(4-pyridiniummethyl)-1,2,3-triazol-1-yl]methyl-6,6-dihydropenicillanate 1,1-dioxide (12a), when tested in combination with piperacillin, showed excellent synergistic activity against microorganisms producing plasmid-mediated enzymes, but had insufficient activity against microorganisms producing chromosomally mediated class I enzymes.