We have studied the efficacy of a continuous paravertebral infusion of bupivacaine for the management of post-thoracotomy pain in 20 infants with a median age of 5.3 weeks (range 2 days to 20 weeks). Immediately before chest closure, 0.25% bupivacaine 1.25 mg kg-1 was injected into an extrapleural paravertebral catheter, inserted under direct vision. A continuous infusion of 0.25% bupivacaine 0.5 mg kg-1 h-1 was commenced 1 h later and terminated after 24 h. We found that extrapleural paravertebral catheter placement under direct vision was easy in neonates and infants. The technique provided effective postoperative pain relief in 18 (90%) patients and the failure in two (10%) infants was attributed to catheter block. Mean maximum serum concentrations of bupivacaine after the loading dose and during infusion were 1.03 (SD 0.56) and 2.00 (0.63) microgram ml-1, respectively. There were no major complications relating to the technique and we conclude that extrapleural paravertebral block is a simple and effective method for post-thoracotomy analgesia in young infants.