Mice were rendered morphine-dependent by the subcutaneous implantation of a pellet containing 75 mg of morphine base; 72 h after the implantation, the animals were injected intraperitoneally either with vehicle or with various doses of delta9-tetrahydrocannabinol, delta8-tetrahydrocannabinol, cannabidiol, cannabinol, or 11-hydroxy-delta8-tetrahydrocannabinol. Thirty minutes after injection of the cannabinoids, the antagonist, naloxone HC1, was administered to induce the stereotyped withdrawal jumping syndrome. The dose of naloxone needed to induce withdrawal jumping in 50% of the animals (ED50) was determined for each dose of the cannabinoids. All of the cannabinoids inhibited the naloxone-precipitated morphine abstinence as evidenced by an increase in the naloxone ED50. Two additional signs of morphine abstinence, defecation and rearing behavior, were also suppressed by the cannabinoids. The relative effectiveness of the cannabinoids in inhibiting morphine abstinence appeared to be in the following order: delta9-tetrahydrocannabinol greater than delta8-tetrahydrocannabinol greater than 11-hydroxy-delta8-tetrahydrocannabinol greater than cannabidiol greater than cannabinol. These data suggest that cannabinoids may be useful in facilitating narcotic detoxification.