A randomised double-blind study was conducted to compare the influence on postoperative pain of equal volumes of one of two concentrations of bupivacaine (0.25%, 0.5%), or saline 0.9%, injected into the knee joint after arthroscopy. The results showed that intra-articular bupivacaine had no significant analgesic effect in either concentration. Plasma bupivacaine concentrations were measured 20 minutes after injection in order to determine the extent of systemic absorption.