1. The properties of a new antihypertensive agent, SK&F 92657, dl-3-[2-(3-t-butylamino-2-hydroxypropoxy)phenyl]-6-hydrazinopyridazine, have been studied.
2. The compound caused a sustained fall in blood pressure in several species as a result of precapillary vasodilatation, particularly in the renal and coronary vasculatures.
3. The β-adrenoreceptor-blocking actions of SK&F 92657 prevent reflex cardiac stimulation.