Serial blood, muscle, and bone concentrations of cephalothin following intravenous infusion were determined in forty-eight patients during total hip replacement. Thirty patients received hypotensive anesthesia and the remaining eighteen received anesthesia without induced hypotension. The concentrations of cephalothin were determined during the first (early) and second (late) hours of the operation. Late serum levels were lower in the patients who had induced hypotension. In all patients at least one bone specimen contained measurable amounts of cephalothin. When pentolinium (Ansolysen) was used to induce hypotension, the late serum and early bone cephalothin concentrations were lower, while use of trimethaphan (Arfonad) did not appear to result in lower cephalothin concentrations in serum, muscle, or bone compared with patients with normotensive anesthesia.