A total of 46 patients aged 59–84 who underwent transurethral resection of the prostate gland received 2 g of ceftriaxone intravenously at different points in time, ranging from 30 min to 74 h before the operation. The antibiotic concentration was determined in the serum as well as in the prostate adenoma tissue using microbiological methods after treating the tissue in a stomacher. 30 min after application, tissue concentrations were between 12.9 and 73.7 μg/g, and after 4 h still between 1.0 and 50.0 μg/g. Even after 48 h levels between 0.6 and 5.6 μg/g were found. Therefore ceftriaxone proved not only to have a long serum half-life as compared to other comparable cephalosporins, but also prolonged tissue concentrations, which justifies a single preoperative dose before transurethral resection of the prostate gland, as established by the clinical results descr