Hypotensive activity of 2-(2-(4-(3-methylphenyl)-1-piperazinyl)ethyl) quinoline (compound 71/73; centhaquin) was studied in cat and rat. The compound lowered the blood pressure and reduced the heart rate of anaesthetized and unanaesthetized (decerebrate) cat in a dose-dependent manner (0.01-1.0 mg/kg i.v. or 1.0-2.5 mg/kg intraduodenally). The hypotensive effect was insignificant in spinal transected cat but more marked in deafferented and vagotomized animals. Localization of centhaquin to brain by intravertebral arterial injection (5-10 micrograms) or by topical application to the exposed ventral surface of medulla or floor of the fourth ventricle caused hypotension and bradycardia as well as reduced the excitability of the vasomotor loci. It was also effective in rats after single as well as multiple dosing. The compound seems to act centrally to reduce the blood pressure.