It is traditionally considered that angiotensin--converting enzyme inhibitor (ACEI) and spironolactone could not be used simultaneously because of the assumed risk of hyperkalemia. However, despite ACEI therapy edema and congestive status remain in some of the patients with severe congestive heart failure (CHF). In order to seek an effective therapy for these patients, we observed the efficacy and safety of captopil plus spironolactone in patients with refractory CHF, with strict monitoring of renal function, serum and urine electrolytes and blood pressure (BP). Thirty-five patients with refractory CHF and New York Heart Association functional class IV without renal dysfunction, hypotension and hyperkalemia, whose plasma aldosterone (ALD) level in 88.6% of them was above normal value, were randomly assigned to group A (n = 16, captopril alone) and B (n = 19, captopril plus spironolactone) for a 4-week treatment. The dosage of both drugs was individually adjusted in time according to the results of serum potassium and renal function. The improvement in dyspnea--fatigue ratings, urinary volume and Na+/K+ ratio in group B was more significant than that in group A, and the plasma ALD level in group B decreased obviously while it remained high in group A after therapy. Two patients in group B who had had normal plasma ALD level with urinary Na+/K+ ratio > 1.0 before the therapy did not exhibit any clinical improvement. A strong negative correlation was found between plasma ALD level and urinary Na+/K+ ratio (correlation coefficient -0.689, P < 0.01). None of the patients had obvious hyperkalemia and hypoaldosteronism.(ABSTRACT TRUNCATED AT 250 WORDS)