Five patients, who had never received any drug treatment but who had severe chronic congestive heart failure with salt and water retention, were studied before and after a single dose of enalapril (10 mg orally). Three patients continued on enalapril as monotherapy (10 mg b.d. orally) for one month. Central haemodynamics, body fluid volumes, renal function and plasma hormones were measured at rest. The initial mean right atrial pressure was 13 +/- 4 mm Hg, pulmonary wedge pressure 29 +/- 4 mm Hg and cardiac index 1.8 +/- 0.21/min/m2. Enalapril, given acutely, caused only small changes. Two patients were withdrawn after the single dose of enalapril and treated with diuretics for clinical reasons. The remaining three patients each lost more than 4 kg in weight after one month of treatment with enalapril alone. Total body exchangeable sodium and total body water were reduced but central haemodynamics were unchanged. Although enalapril was of some benefit when given alone to patients with severe congestive heart failure, all five patients were finally treated with diuretics for clinical reasons. Enalapril is not recommended as the initial and only therapy for patients with severe congestive heart failure.