In 5 patients with respiratory tract infections, concentrations of cefotetan (CTT) in serum and sputum after 1 hour intravenous administration of 2 g of CTT to each patient were investigated, and following results were obtained. Serum levels of CTT The mean peak level of CTT was 232.0 +/- 16.2 micrograms/ml immediately after the 1 hour drip infusion, then declined gradually and was 48.0 +/- 8.8 micrograms/ml after 6 hours. Sputum levels of CTT Mean sputum levels of CTT were 2.15 +/- 0.19 micrograms/ml from 2 to 4 hours after the administration and 2.19 +/- 0.18 micrograms/ml from 4 to 6 hours. Clinical evaluation of CTT Clinical effects were excellent in 1 case, good in 3 cases and poor in 1 case. No side effects were observed.