In the past 10 to 20 years the pneumococcus, the most common pathogen of community-acquired pneumonia, has developed resistance to most antibiotics used for its treatment. Classes with important resistance problems include the beta-lactams, the macrolides and lincosamides, trimethoprim-sulfamethoxazole, and the tetracyclines. Unfortunately, resistance to more than one class of antibiotics is common in pneumococci, and their treatment is thus becoming more difficult. Patients likely to harbour resistant organisms include young children, particularly those attending day care, older patients, and subjects who have received recent antibiotic therapy, suffer from underlying diseases including HIV, or have nosocomial or polymicrobial pneumonia. The consequences of resistance development are different for different classes of antibiotics. With beta-lactams, the increase in minimal inhibitory concentrations is usually moderate in resistant strains, and because of the high concentrations that can be achieved with this class of drugs resistance does not usually lead to treatment failure. Thus, beta-lactams continue to be important drugs for the treatment of pneumococcal pneumonia, even if the organism is resistant. In contrast, resistance to other classes of antibiotics must be assumed to render these drugs ineffective. Newer quinolones represent valuable alternatives for the treatment of pneumococcal pneumonia, since their efficacy is not affected by resistance to other classes of antibiotics and they cover almost all pathogens of community-acquired pneumonia, including the atypical pathogens. However, they should be used with restraint in order to preserve this valuable class of drugs.