In this study 13 patients with a history of chronic respiratory disease were treated with temocillin for severe infection of the lower respiratory tract. Eleven patients were clinically improved or cured at the end of treatment and 4 remained free of infection at follow up. However, the 2 remaining patients failed to respond clinically and bacteriologically to temocillin. Blood and sputum pharmacokinetics were studied in patients receiving temocillin at 12-hourly intervals in doses of either 1g by intravenous bolus or 2g by intravenous infusion. On the first day of treatment the mean peak serum concentration was 102 mg/L for the 1g dose and 220 mg/L for the 2g dose, falling to 11 mg/L (1g) and 18.8 mg/L (2g) at 12 hours. Similar results were recorded on the last day of treatment. Temocillin concentrations in the sputum ranged from 1.5 to 2.8 mg/L, with no difference being found in the sputum concentrations of the 2 doses. Temocillin was well tolerated and was found to be an effective treatment for Gram-negative bacterial infections of the lower respiratory tract.