The objective of this study was to evaluate the concentration in the bronchial secretions of a new injectable cephalosporin, cefotiam, which is characterized by an excellent antibacterial activity, stability against beta-lactamases and interesting pharmacokinetic properties. 30 patients suffering from acute exacerbation of a chronic bronchitis or bronchiectasis with expectoration, received either 1 g i. v. of cefotiam in a single dose or four doses of 1 g each over a period of 3 days. The bronchial secretion samples were obtained by fibroscopy, 1, 2, or 4 h after the last dose, in order to evaluate the kinetics of the bronchial concentration of cefotiam. Blood samples were taken simultaneously in order to establish a possible correlation between the bronchial and serum levels of the drug. The results of the study show a rapid and significant transfer of the drug through the bronchoalveolar capillaries, elevated bronchial concentrations starting from the 2nd h, reaching 10 micrograms/ml (or more) in certain cases, slow elimination with bronchial concentrations persisting at high levels for up to 4 h and a ratio between bronchial and serum concentrations of 25-60% at the 2nd h and more than 100% at the 3rd and 4th h. These results confirm the excellent diffusion of cefotiam, especially in the respiratory tract, allowing bronchial levels largely superior to the minimum inhibitory concentrations required to kill the bacteria usually responsible for lower respiratory tract infections.