2 g ceftizoxime were administered as a i.v. bolus injection to 34 patients, in whom a lung operation was performed for either therapeutic or diagnostic reasons. At different time intervals after the injection, a lung biopsy was taken together with a serum sample to measure the antibiotic concentrations. The serum concentrations of ceftizoxime in these patients differed only slightly from results obtained with healthy volunteers. 60 min after injection, ceftizoxime-concentrations in the lung tissue varied between 7 and 15 micrograms/g (mean 11, n = 4) and declined slowly thereafter. After 4 h in two patients values of 2 and 4 micrograms/g ceftizoxime, respectively, were obtained. Even after 7 h concentrations of more than 1 microgram/g tissue were found.