We have studied the efficacy of prolonged, continuous paravertebral infusion of bupivacaine for the management of post-thoracotomy pain in 22 infants with a median age of 1.5 weeks (range 1 day to 20.4 weeks). Immediately before chest closure, 0.25% bupivacaine 1.25 mg kg-1 was given into an extrapleural paravertebral catheter, inserted under direct vision. Subsequently, 0.125% bupivacaine with adrenaline 1:400000 was infused at a rate of 0.2 ml kg-1 h-1 for 48 h. We confirmed that extrapleural paravertebral catheter placement under direct vision was easy in neonates and infants. The technique provided effective post-operative pain relief in 86% of patients, with three patients requiring morphine in addition. Mean serum concentration of bupivacaine after 48 h was 1.60 (0.67) micrograms ml-1, but bupivacaine concentrations > 3 micrograms ml-1 were found in three patients at 30-48 h. There were no major complications relating to the technique, and paravertebral block was an effective method of providing prolonged post-thoracotomy analgesia in these young infants.