Since the introduction of cephalothin and cephaloridine as the first parenteral cephalosporins and cephalexin as the first member of the group which is absorbed from the gastrointestinal tract, several new cephalosporin derivatives have been developed. Most of these have no major advantages over cephalothin, cephaloridine or cephalexin. Increased knowledge about the importance of beta-lactamases for bacterial resistance against beta-lactam antibiotics has focused interest on development of drugs with increased resistance to degradation by these enzymes. Among the caphalosporins, cefamandole and cefuroxime have been found to be markedly more active against beta-lactamase producing Gram-negative bacteria. A new group of beta-lactam antibiotics, the cephamycins, have been introduced with cefoxitin as the first clinically useful member. Cefoxitin has the spectrum of a beta-lactamase-resistant cephalosporin and is also active against Bacteroides fragilis. The review concentrates on the antibacterial spectrum of these three new antibiotics and on their clinical efficacy.