The fluoroquinolones are a new class of antimicrobial agents structurally related to nalidixic acid. They have a broad spectrum of activity against pathogens, including Pseudomonas aeruginosa, other multiresistant gram-negative bacteria, and methicillin-resistant Staphylococcus aureus but not anaerobes. They are well absorbed after oral administration, and some achieve serum and tissue levels well exceeding the minimal inhibitory concentrations for susceptible bacteria. Adverse reactions are rare, and when they occur they are usually mild. Use of quinolones should be avoided in children because of possible damage to developing cartilage. These agents should prove useful in the treatment of urinary tract infections caused by bacteria resistant to other oral agents, bacterial gastroenteritis, and gonococcal infections. The use of quinolones may potentially reduce the cost of treatment of certain systemic infections caused by multiantimicrobial resistant organisms because outpatient oral therapy is possible.