A variety of new beta-lactam antibiotics is in use today. A considerable number of new penicillins have extended spectra which include Pseudomonas and Klebsiella spp. and other important nosocomial organisms. In addition, clavulanic acid, a beta-lactamase inhibitor, has been added to some of these compounds to enhance further their spectrum against Staphylococcus aureus and other bacteria. The first-, second- and third-generation cephalosporins are described. Second-generation cephalosporins have an extended spectrum, covering Gram-negative organisms. Third-generation compounds have both improved beta-lactamase stability and better Gram-negative cover. Other types of beta-lactam antibiotics have recently been developed, such as imipenem and aztreonam, which also have broad activity against Gram-negative bacteria.