The duration of postoperative analgesia following femoral nerve block with a catheter technique was studied. Intermittent doses of bupivacaine were given to 208 consecutive patients presenting for open repair of the anterior cruciate ligament, initially 0.5% and thereafter 0.25% 0.4 ml/kg 2-4 times daily. Supplementary analgesia with piritramide 0.15 mg/kg I.M. was provided 4-6 hourly as required and the number of analgesic demands recorded. Based on the duration of analgesia and on the number of analgesic demands required, good or satisfactory analgesia was obtained in 88% of the patients. The catheter remained an average of 2.8 days in position and no infectious or irreversible neurological complications were seen. It is concluded that femoral nerve block using a catheter technique, provides safe and reliable analgesia, improves patient mobility, has a high patient acceptance and is capable of reducing systemic analgesic demand following anterior cruciate ligament repair.