The fluoroquinolones represent an important addition to the antimicrobial armamentarium. They are, however, commonly overused. It is estimated that in 1989, ciprofloxacin was prescribed for 1 in every 44 Americans. This observation demonstrates not only the overusage, but the economic incentive for development of additional fluoroquinolones. In some situations, oral fluoroquinolone therapy can reduce costs by eliminating the need for parenteral therapy and reducing the need for or the duration of hospitalization. In most situations where oral antimicrobial agents are being considered, however, the fluoroquinolones are among the most expensive alternatives. In addition to concerns about cost factors, it is important to reiterate concern that widespread overuse of these agents will promote the development of microbial resistance and ultimately limit their usefulness. The clinical usefulness of the fluoroquinolones is summarized in Table 4. As can be seen, the fluoroquinolones are the "possibly preferred agent" in very few infections: complicated urinary tract infections due to Gram-negative bacilli resistant to other oral antimicrobial agents, severe bacterial gastroenteritis, exacerbations of lower respiratory tract infection in patients with cystic fibrosis, osteomyelitis due to Gram-negative bacilli sensitive to the fluoroquinolones, and invasive external otitis. They are alternative agents in a number of other infections when sensitive Gram-negative bacilli are the identified pathogens. A considerable literature exists on using these agents in these and other circumstances, but one must remain wary of limited reports of efficacy in comparison to known efficacy of established and less expensive agents.(ABSTRACT TRUNCATED AT 250 WORDS)