Cadralazine is an antihypertensive of the hydrazinophthalazine chemical class. In hypertensive patients the optimal effect, based on the antihypertensive efficacy to tolerability ratio, is seen after a 15 mg dose when the drug is administered as monotherapy. When administered in combination with other antihypertensive agents, a 10 mg daily dosage seems appropriate. Noncomparative trials have shown that, in patients who had failed to respond adequately to a beta-blocker and/or diuretic, the addition of cadralazine 10 to 30 mg once daily reduced systolic/diastolic blood pressure by 11 to 19%/13 to 22%. This antihypertensive effect becomes evident over a 2- to 6-week period of therapy and persists during longer term administration. Comparative studies have shown that cadralazine is superior to placebo, and has a similar blood pressure lowering effect to hydralazine, dihydralazine and prazosin in patients not controlled by beta-blocker and/or diuretic but who continued to receive these treatments. Similarly, cadralazine and chlorthalidone were equally effective in reducing blood pressure in resting hypertensive patients but cadralazine shows an advantage in reducing the pressor response in exercising patients. Cadralazine is well tolerated when administered with a beta-blocker or diuretic. Most adverse effects become less frequent and severe with continued use, occur more frequently at dosages of 20 mg/day or more, and do not generally require withdrawal of therapy. Manifestations of the drug's vasodilating properties such as headache, asthenia, dizziness, palpitations and flushing are the most commonly reported symptoms during cadralazine monotherapy, but these may be reduced during combination therapy. The drug does not appear to induce a systemic lupus-like erythematosus syndrome, as may occur with hydralazine, but additional clinical experience is required to completely exclude this possibility. The therapeutic potential of cadralazine cannot be clearly established until the present limited clinical base is expanded to include comparisons with other classes of vasodilating drugs (ACE inhibitors and calcium antagonists), and its utility in the management of other indications such as severe hypertension during pregnancy has been adequately explored.