This study determined the efficacy of intravenous ciprofloxacin in the treatment of institutionalized patients with lower respiratory tract infections. Hospitalized adults with hospital/nursing home-acquired pneumonia were randomly assigned to receive either intravenous ciprofloxacin or ceftazidime. When deemed feasible, therapy was changed to oral ciprofloxacin for patients who received ciprofloxacin intravenously or to any alternative oral therapy for patients who received ceftazidime. All 23 patients who received ciprofloxacin had a favorable response versus 15 of 21 patients who received ceftazidime (p less than 0.025). One patient with a favorable response to ceftazidime developed a superinfection and one patient had a relapse during subsequent alternative oral therapy. However, patients who received ceftazidime were more severely ill than those who received ciprofloxacin on the basis of APACHE II scores.