CAM--a new type of opiate antagonist [10, 11] was used to study the types of opiate receptors (OR) involved in the analgesic and narcosis potentiating effects of different opiates. The analgesic assays were: hot plate, algolytic test (rat) and acetic acid stretching test (mouse). 2. The in vivo equivalent of pA2 value (apparent pA2) for naloxone (NX) and CAM was determined with each opiate agonists. 3. The estimated pA2 values for analgesia did not differ significantly from those obtained for anesthesia in the case of NX, however, if CAM was used as antagonist the pA2 values were the same as with NX in the algolytic test, but different result was obtained when analgesia was measured by hot plate and stretching test, and narcosis potentiation was examined. 4. It was concluded that NX and CAM interact with the same OR when algolytic test was used, however different type of OR might be involved in hot plate and stretching assays and anesthesia potentiation, too.
