Imipenem is a new beta-lactam which differs chemically from penicillins and cephalosporins but has a similar mode of action. It is a potent antibacterial agent with a broad spectrum of activity encompassing both aerobes and anaerobes. However, in vitro, it does not appear to offer a great improvement over other available agents for the treatment of infections caused by problem organisms such as Pseudomonas aeruginosa, methicillin-resistant Staphylococcus aureus and enterococci. The results of clinical trials suggest that imipenem is efficacious and toxic side effects do not appear to be a problem.