The efficacy and safety of routine use of adjusted low-dose warfarin for twelve weeks--without sonography or venography--for the prophylaxis of deep-vein thrombosis after total hip replacement was assessed in 268 patients (134 men and 134 women) who were between the ages of forty and eighty-five years (average, sixty-one years). The patients were given warfarin orally both before and after the operation. The initial dose was usually ten milligrams on the night before the operation and five milligrams on the night after the operation. Thereafter, the dose was adjusted to keep the prothrombin time between fourteen and sixteen seconds. The control time was ten to twelve seconds. The partial thromboplastin time was also measured, and the dose of warfarin was reduced if the value was more than fifty seconds. All 268 patients continued to take low-dose warfarin for twelve weeks after the operation. There were 170 primary and ninety-eight revisional total hip-replacement operations. Thirty-four patients (13 per cent) had a history of thromboembolic disease or venous stasis in a lower limb. Neither phlebography nor sonography was done routinely. All of the patients were followed for six months after the operation. There were no fatal pulmonary emboli during the period of the study and no known pulmonary emboli after any patient was discharged from the hospital. Two non-fatal pulmonary emboli were identified, both during hospitalization. Ten patients (4 per cent) had an episode of major bleeding--a wound hematoma in nine and a gastrointestinal hemorrhage in one--during hospitalization.(ABSTRACT TRUNCATED AT 250 WORDS)