In a double blind, randomised, controlled investigation the analgesic effect of a continuous block of the lumbar plexus with bupivacaine compared with sodium chloride was examined in 20 patients with postoperative pain after knee-joint surgery. The infusion was given through a catheter inserted in the neurovascular fascial sheath of the femoral nerve, according to the three-in-one block technique. The patients treated with bupivacaine had significantly lower pain scores and a significantly lower demand for morphine. Side effects related to the catheters or the infusions of bupivacaine were not observed.