Morphine (20 and 40 µg/kg) administered into the cerebral ventricle of conscious sheep caused significant inhibition of the mean frequency and the average amplitude of primary ruminal contractions by 45 min after injection. Between 90 and 120 min, morphine (40 µg) provoked a significant increase in the amplitude (p<0.01). At both doses it caused strong psychomotor excitability that lasted for more than 140 min. Isolation of the hypothalamus prevented both the inhibitory effects of morphine on rumen motility and the drug-induced psychomotor excitability. Histopathological analysis of slices of the hypothalamus, pons and medulla indicated descending degenerative changes in the nervous pathways connecting the hypothalamus with lower structures in the brain. These results suggest either that hypothalamic isolation caused degeneration of inhibitory descending pathways that connect the hypothalamus with the gastric centres or that structures of importance for forestomach motility are not located within the gastric centres but elsewhere in the brain, for example in the hypothalamus.