Two controlled clinical trials compared loracarbef (LY163892 with amoxicillin/clavulanate or amoxicillin in the treatment of acute exacerbations of chronic bronchitis. Collectively, of 1,057 patients enrolled, 390 qualified for analysis: group 1 comprised 200 patients treated with loracarbef (400 mg twice daily); group 2, 120 patients treated with amoxicillin/clavulanate (500 mg three times daily); and group 3, 70 patients treated with amoxicillin (500 mg three times daily). Symptomatic and bacteriologic outcomes were assessed at post-therapy (within 72 hours of therapy completion), and at late-posttherapy (10-14 days after therapy completion). These evaluations were combined to provide an "overall" evaluation that accounted for all unfavorable outcomes occurring at either the posttherapy or late-posttherapy visit. At the posttherapy evaluation, 93.0% of group 1 patients, 95.0% of group 2 patients, and 88.6% of group 3 patients demonstrated favorable clinical outcomes (cure or improvement). "Overall" favorable clinical outcomes were achieved in 88.0% of group 1 patients, 90.0% of group 2 patients, and 81.4% of group 3 patients. Bacteriologic results from the two studies could not be merged due to marked differences in how posttherapy bacteriologic results were assessed. The clinical significance of positive posttherapy sputum cultures was doubtful: 90% of patients with a positive sputum culture at the posttherapy visit who returned for the late-posttherapy visit had successful clinical outcomes documented at the late-posttherapy evaluation. Loracarbef was associated with a lower incidence of diarrhea and a higher incidence of headache as compared with amoxicillin/clavulanate. These results suggest that 400 mg loracarbef twice daily for 7 days is effective and safe in the treatment of acute exacerbations of chronic bronchitis.