An increasing number of new cephalosporins continue to become available in the clinic so that the clinician requires something akin to Ariadne's thread to work through the labyrinth of confusing names and product claims. The parenteral cephalosporins may be grouped on the basis of structure, antimicrobial activity and metabolic stability as follows: 1. cephacetrile, cephalothin, cefapirin; 2. cefotaxime; 3. cephaloridine, cefazedone, cefazolin, cefotiam; 4. cefamandole, cefoperazone, cefsulodin, cefuroxime, cefoxitin, ceftazidime, ceftizoxime, ceftriaxone, lamoxactam. Groups 2 and 4 contain the most interesting compounds in terms of their biological activity and therapeutic significance. Even carbenicillin-resistant strains of Pseudomonas aeruginosa are inhibited by one of the recent broad-spectrum cephalosporins. In the clinic, minor differences between the highly active cephalosporins are not likely to be of therapeutic significance.