In 48 patients undergoing elective gynecological, urological and otorhinolaryngological surgery a pharmacokinetic study after 1 g dose of ceftriaxone or cefotaxime was done. Concentrations of the two antibiotics were studied in interstitial fluid with the suction blister technique and in some tissues collected during the operation. The mean tissue levels were generally higher after ceftriaxone administration than after cefotaxime and for both drugs they were lower than the contemporary drug levels in interstitial fluid. However at the concentrations found almost all aerobic and anaerobic bacteria causing postoperative wound infections are inhibited.