1 or 2 g doses of cefodizime i.m. were studied in 287 patients admitted to hospital with acute purulent exacerbations of chronic bronchitis, mostly associated with Haemophilus influenzae, Streptococcus pneumoniae or Moraxella catarrhalis. Pharmacokinetic studies in serum and sputum on the first treatment day yielded mean peak serum concentrations of 50 to 100 mg/l, with corresponding sputum concentrations of 1.4 and 2.7 mg/l, after the two respective doses. No great differences were found between the clinical and microbiological results in the various dosage groups, and no corresponding improvement was noted with the highest dosages studied. In general, infection was eliminated in 90 to 95% of patients at the end of treatment, and in approximately 70 to 80% after a follow-up week. Some infections associated with beta-lactamase producing M. catarrhalis persisted or relapsed after treatment. Unwanted drug effects were recorded in five patients, leading to discontinuation in two. It is concluded that a single daily intramuscular dose of 1 g cefodizime for seven days produces satisfactory results in most patients.