To compare the efficacy and safety of five-day cefdinir treatment with seven-day loracarbef treatment in patients with acute exacerbations of chronic bronchitis, 586 patients were enrolled in a multicentre, randomised, double-blind trial. Patients received either five days of treatment with cefdinir (n = 291) at 300 mg twice daily or seven days of treatment with loracarbef (n = 295) at 400 mg twice daily. Microbiological assessments were done on sputum specimens obtained at admission and at the two post-therapy visits, if available. The clinical cure rates were 86% (138/160) and 85% (141/166) for the evaluable patients treated with cefdinir and loracarbef, respectively. Respiratory tract pathogens were isolated from 457 (78%) of 586 admission sputum specimens, with the predominant pathogens being Haemophilus parainfluenzae, H. influenzae, Moraxella catarrhalis and Staphylococcus aureus. The microbiological eradication rates at the test-of-cure visit were 88% (193/219 pathogens) and 90% (227/251 pathogens) for the evaluable patients treated with cefdinir and loracarbef, respectively. Adverse event rates while on treatment were 30% and 21% for cefdinir- and loracarbef-treated patients, respectively. These results indicate that a five-day regimen of cefdinir is effective and safe for the treatment of patients with acute exacerbations of chronic bronchitis.