Thirty hospital in-patients with acute purulent exacerbations of chronic bronchitis were treated with 1 g cefotaxime intramuscularly twice daily for 10 days: 3 dropped out A further 10 patients received 2 g twice daily. Blood and sputum conconcentration studies showed that the sputum levels following 1 g doses averaged 0.57 mg/l with mean peak serum concentrations of 37.6 mg/l. After 2 g, the corresponding figures were 1.84 and 54 mg/l, respectively, which can be related to the usual MIC for Haemophilus influenzae strains of 0.03 mg/l or less. The clinical results were excellent in 21 patients and good in the remaining 6 given 2 × 1 g doses, but all the 10 patients given 2 × 2 g showed excellent results. Reinfections occurred after treatment in 6 of the 27 patients who received 1 g doses, but were not encountered in any of those given 2 g. These results can be considered exceptionally good.