One hundred and seventy-four consecutive patients with symptoms of derangement of the knee were examined with an arthroscope under local anaesthesia using a continuous pressure-irrigation system. A 0.2 per cent prilocaine-saline solution was used as irrigation fluid. In the first 19 patients the serum level of prilocaine was monitored for six hours after the start of irrigation. Eighteen of the 174 patients had a transcutaneous partial meniscectomy at the same time as the examination. All the patients tolerated the examination well. The distension of the knee produced by the pressure-irrigation system provided a high degree of diagnostic accuracy. The serum levels of prilocaine were low throughout the monitoring period reaching a mean peak value of 0.28 micrograms per millilitre after one hour. There were no adverse side-effects. This technique provides a safe and efficient method to meet the increasing demands of arthroscopic procedures of the knee.