We reviewed the spectrum of activity, pharmacokinetics, clinical efficacy, adverse effects, and relative advantages of piperacillin-tazobactam, a new beta-lactam-beta-lactamase inhibitor. Piperacillin-tazobactam has a wide spectrum of activity that includes gram-positive organisms such as staphylococci and streptococci, as well as many gram-negative aerobic and anaerobic bacteria. The combination distributes rapidly after parenteral administration and penetrates well into skin, lung, and intestinal mucosa. Compared with other beta-lactam-beta-lactamase inhibitor combinations, piperacillin-tazobactam has comparable efficacy in the treatment of intraabdominal infections, skin and soft tissue infections, and upper and lower respiratory tract infections. It may have better in vitro activity than the currently available combinations against selective bacteria that produce class I beta-lactamases (Richmond-Sykes classification). The combination is well tolerated, with diarrhea being the most common reported adverse effect. Additional controlled trials and clinical experience are required to define its role in clinical practice.