A variety of N-(alkyl/alkenyl/aryl-N-heterocyclic ureas and thioureas were synthesized as potential antihypertensives. The selected heterocyclic nuclei were the 6-substituted quinoline and the pyridine. Eleven synthesized compounds and seven related compounds in the series were evaluated orally at a dose of 100 mg/kg in conscious deoxycorticosterone acetate/saline-treated hypertensive rats by the tail-cuff method. Seventeen out of the eighteen tested compounds possessed significant antihypertensive activity (p < 0.05). 1-n-Propyl-3-[2'-(6-methoxy)quinolyl]urea (9), showing 29.1% reduction in systolic blood pressure, was the most active compound in the series. Two other compounds producing a fall in systolic blood pressure of the same magnitude were 1-allyl-3-[2'-(6-methyl)quinolyl]thiourea (4) and 1-n-propyl-3-[(2'-pyridyl)methyl]urea (17). Compound 17 with rapid onset caused significant relaxation (p < 0.01) of isolated rabbit femoral artery and guinea pig atrium but had no effect on heart rate. However, none of these exhibited higher potency than prazosin (5 mg/kg). The potency, onset, and duration of action improved when the heterocyclic nucleus was pyridine.