Following peripheral administration the purported dopamine (DA) agonist (3,4-dihydroxyphenylimino)-2-imidazolidine (DPI) was shown to increase the diastolic blood pressure of pithed rats and to decrease rat motility and rectal temperature. Dose-effect relationships were established and half-maximal effective doses for the hypertensive and hypothermic response to DPI were calculated to be 4.4 nmol/kg i.v. and 2.0 mumol/kg i.p., respectively. Pretreatment with various antagonists revealed that both alpha 1- and alpha 2-adrenergic mechanisms were responsible for the DPI-induced hypertension, hypomotility and hypothermia, indicating that DPI acts as a non-selective alpha-adrenoceptor agonist. Qualitatively the DPI-induced effects were found to correlate well with those reported for its structural analogue clonidine, thus suggesting a similar mechanism of action for these agents. DA receptor antagonists appeared to lack inhibitory potency towards any of DPI-elicited responses. The results do not therefore support the designation of DPI as a DA receptor agonist.