Previous studies have shown that chronic intrathecal cannulation can interfere with the homeostasis of central opioid peptides. These results show that beta-endorphin and Met-enkephalin concentrations did not change in the hypothalamus of rats bearing a chronic cannula inserted between C8-T1 up to L3 and fixed to the processes transversus T1. These results suggest that chronically cannulated rats can be considered as normal when studying hypothalamic beta-endorphin or Met-enkephalin concentrations, and used in physiological studies, depending on the technique employed.