In the closing decade of the last century, we saw warnings that infectious diseases will require much more attention from patients and physicians in the 21 st century. Recently d- covered diseases such as AIDS pose a major threat to the population at large, and to that threat has been added the re-emergence of established pathogens, microbes that were re- ily treatable in the past. Since infectious diseases already play a major role in the burden of illness and mortality, health care providers and planners are worried. A large proportion of the problem is man-made, arising mainly from the unnecessary overuse of antimicrobials in hospital and community settings and from the agricultural misuse of the agents in animal feed. A consequence has been a dramatic increase in resi- ant strains of bacteria that were considered conquerable several decades ago. Community infections caused by multi-resistant pneumococci serve as an example. These organisms were readily treated with penicillin, but now the spread of penicillin-resistant Strepoccus pneumoniae from continent to continent is becoming a worldwide problem. This is a major concern because pneumococcal infections are common in the community, being the le- ing cause of pneumonia, sinusitis, and meningitis. Resistant bacteria in hospitals are also becoming more prevalent. We have become accustomed to hearing about methicill- resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE), but now we have to be concerned about multidrug-resistant coliform bacteria and pseudomonads.