Dose-response curves of three receptor-selective opioids were established in a Group of nonburned and a group of burned rats. Morphine (p-agonist), biphalin(μ and δ agonist), and U50488H (K-agonist) were administered to each group, and analgesia was mea-sured by tail flick latency testing. Each opioid had a significant increase in potency (i.e., a decrease in EDso values) in the burned (15% body surface area) compared with the nonbumed groups. Moderate doses of each drug (i.e., EDm doses estimated from nonbumed group data) in each case augmented stress-induced analgesia in the burned group. Analgesic doses faiied to prevent a significant increase in plasma pendorphin and corticosterone after larger surface area (25%) bums. Regardless of receptor specificity, opioid analgesic potency is increased acutely after burn injuries.