Ampicillin/sulbactam (1 to 2 g ampicillin and 0.5 to 1 g sulbactam, administered intravenously once every 6 hours) and cefuroxime (750 mg to 1.5 g, administered intravenously once every 8 hours) were compared to determine their efficacy and safety in treating patients with lower respiratory tract infections of bacterial etiology. Nineteen of the 41 patients treated with ampicillin/sulbactam and 18 of the 44 patients treated with cefuroxime were assessable for efficacy. The clinical responses to the 2 treatments were comparable: 5 (26%) patients treated with ampicillin/sulbactam were cured and 14 (74%) were improved. Five (28%) patients who received cefuroxime were cured, 12 (67%) were improved, and treatment failed in 1 patient (6%) (P = 0.569). Similarly, no significant difference was noted between the bacteriologic responses to the two antimicrobials (P = 0.486). All isolates from the patients treated with ampicillin/sulbactam were eradicated, as were all isolates in 17 (94%) of the patients treated with cefuroxime. A superinfection occurred in 1 (6%) patient who received cefuroxime. Adverse reactions were rare and occurred in 3 patients from each treatment group.