The effect of intrapleural bupivacaine in the treatment of post-thoracotomy pain was evaluated. Bupivacaine, 0.5% 20 ml, with adrenaline (5 micrograms/ml) was given through an indwelling intrapleural catheter, at 4-h intervals four times daily for 2 days. No pleural suction was applied during and 10 min after each injection. A control group received intramuscular oxycodone on request. A visual analogue scale (VAS), a pain questionnaire (PQ) and registration of the need for supplementary analgesics were used for the assessment of postoperative analgesia. Blood-gas analyses showed elevated PaCO2 values in both groups on the day of operation and on the first postoperative day, without differences between the groups. Plasma concentrations of bupivacaine did not reach toxic values, and no symptoms of central nervous toxicity or any other untoward reactions were found during the study period. Clinically, there was some pain relief after the intrapleural bupivacaine. The VAS and PQ scores 30 min after bupivacaine instillations diminished to an extent similar to that after oxycodone treatment. The need for analgesics during the day of operation was less in the bupivacaine group than in the control group (P less than 0.001). The number of oxycodone supplementation doses during 48 h postoperatively was, however, not smaller in the bupivacaine group than in the control group.