Male rats were implanted subcutaneously with a pellet containg 75 milligrams of morphine base or placebo, and naloxone hydrochloride (4 milligrams per kilogram of body weight) was administered 72 hours later. Treatment with delta-9-tetrahydrocannabinol (2, 5, or 10 milligrams per kilogram) 1 hour before maloxone administration significantly reduced the intensity of abstinence; the two higher doses blocked the appearance of wet shakes and escapes, diarrhea, and increased defecation. delta-9-Tetrahydrocannabinol did not induce abstinence itself, and prior treatment with cannabidiol was ineffective in reducing naloxoneprecipitated abstinence in animals with morphine pellets. These data suggest that delta-9-tetrahydrocannabinol may be of value in facilitating narcotic detoxification.