To test the effectiveness of analgesics after thermal trauma, butorphanol, a predominately opioid kappa-receptor agonist, and morphine, a mu-agonist, were administered alone and in combination 2 days after rats were subjected to scald burn or sham burn. After graded doses of morphine were administered, analgesia, assessed by tail flick latency and tail pinch latency, was similar in the sham-burn and scald-burn rats. With butorphanol alone analgesic effects were greater in the scald-burn than the sham-burn rats. When graded doses of butorphanol were given with a fixed dose of morphine (0.5 mg/kg), the tail pinch latency response was less in scald-burn rats and markedly less in sham-burn rats. The tail flick latency responses, however, moved in opposite directions in sham-burn and scald-burn rats receiving the drug combination: in sham-burn rats, tail flick latency effects were the same as with butorphanol alone; whereas in scald-burn rats, tail flick latency increases were suppressed except at the lowest dose.