Immersion of pentobarbital-anesthetized rats into water elicits repetitive shaking movements. These wet shakes are similar to the shaking behavior characteristics of the morphine abstinence syndrome in rats. Morphine sulphate, 10 mg/kg i.p., completely inhibited the wet shake response of normal rats to ice water (2 to 6°C). The inhibitory action of morphine on wet shakes was diminished in rats rendered tolerant to morphine by subcutaneous implantation of a morphine pellet for 3 days. Transverse brain lesions, made bilaterally with an iridectomy knife in anesthetized, non-tolerant rats, completely inhibited the wet shake response to ice water when the transection was made at the mid-collicular level. Lesions at the mid-thalamic level did not significantly affect the wet shake response. It is postulated that the shaking response of morphine abstinence and the wet shake response of normal rats to ice water may share common neural pathways.