A group of antibiotics that are effective in eradicating streptococcal, pneumococcal, staphylococcal, Klebsiella, Neisseria, enteric gram-negative rod bacteria that produce pulmonary, skin and soft tissue, bone and joint, endocardial, surgical, urinary, and bacteremic infections. They have been used most often in a preventive or prophylactic fashion at the time of various surgical procedures. The pharmacology of the early cephalosporins was such that the agents had to be administered by vein in frequent intervals in serious infections. This problem was overcome since most of the newer agents have much longer half-lives. All the third-generation cephalosporins penetrate well into tissues, and antibacterially active levels in various body fluids (pleural, peritoneal, synovial, biliary) and tissues such as bone are excellent. The toxic potential of the agents, considering their broad antibacterial spectrum, has been minor. Toxicities which are seen are those of bleeding due to vitamin K depletion.