In vitro studies of quinolones against intracellular pathogens responsible for lower respiratory tract infections have shown that growth inhibition varies with the strain and with the drug. Following administration of quinolones, drug levels in the lower respiratory tract are similar to or greater than serum levels. Quinolones penetrate readily into cells. The effectiveness of quinolones in lower respiratory tract infections has been demonstrated in both in vitro intracellular infection models and in vivo animal models. These data show that quinolones are a valid therapeutic alternative for lower respiratory tract infections due to intracellular organisms.