Cefoperazone is a third-generation semisynthetic injectable cephalosporin. It has been reported that cefoperazone has beta-lactamase resistance and quite a broad antimicrobial spectrum against many Gram-positive and Gram-negative microorganisms and most anaerobes. In this study, the pharmacokinetics of cefoperazone were examined in a group of 10 patients suffering from acute exacerbations of chronic bronchitis, with purulent or mucopurulent expectorations. Cefoperazone was administered at the dose of 1 g i.m. every 12 hours. Serum and urinary parameters and the profile of bronchial mucus diffusion were assessed after the first administration and during the whole period of treatment which lasted for 7 days. In a second, third, and fourth group of volunteer patients who had to undergo surgical operations, bone, lung and prostatic penetration of cefoperazone was determined in correlation with serum levels.