Cardiovascular and respiratory activity of mu, delta and kappa opioid agonists were investigated utilizing microinjections into the n. preopticus medialis (POM) and periventricularis hypothalami (HPV) of anesthetized rats. Injections of the relative mu agonists Morphine and Morphiceptin the delta agonist D-Ala2, D-Leu5-Enkephalin (DADL) or the putative kappa agonist Dynorphin 1-13 into the HPV caused hypotension and bradypnea; Morphine produced tachycardia while DADL and Dynorphin bradycardia. In the POM, injections of Morphine or DADL increased blood pressure and heart rate whereas Dynorphin caused hypotension and bradycardia. At this site, the mu agonist D-Ala2-MePhe4-Gly5-ol-Enkephalin (DAGO) produced hypotension, tachycardia and bradypnea, DAGO and DADL but not Morphine or Dynorphin also caused bradypnea in this region. These data show that the central cardiovascular and respiratory effects of opioids vary according to injection site and opioid subtype and may differ from findings obtained using cerebroventricular injections.