The antibiotic piperacillin/tazobactam has recently been licensed for use in Denmark. Piperacillin/tazobactam combines a well known beta-lactam antibiotitic, piperacillin, and an inhibitor of bacterial beta-lactamase, tazobactam. The combination of piperacillin and tazobactam compared to piperacillin alone has an expanded antimicrobial spectrum, which includes Klebsiellae, Escherichia coli, and Proteus vulgaris resistant to ampicillin, as well as beta-lactamase-producing Staphylococcus aureus. As piperacillin in itself possesses antimicrobial activity against streptococci, enterococci, and Pseudomonas aeruginosa, the antimicrobial activity of piperacillin/tazobactam indicates that the combination may constitute an alternative to third generation cephalosporins and carbapenems in the treatment of complicated intra-abdominal infections infections in critically ill patients and for the empirical treatment of acute neutropenic febrile patients, as indicated by clinical studies.