Cardiac hypertrophy consequent to renovascular hypertension was investigated in two-kidney one-clip Goldblatt rats. Ventricular weight in renal hypertensive rats correlated closely with level of arterial pressure (r = 0.93, P less than 0.001). DNA, RNA and hydroxyproline contents of the hypertrophied hearts were higher than sham control, but there was no significant change in myocardial concentration of any of them. Surgical treatment (removal of clipped kidney) as well as medical therapy (inhibition of converting enzyme with orally administered captopril, 150 mg/l drinking water) led to reduction of ventricular weight (2.70 +/- 0.01 and 2.78 +/- 0.06, respectively, vs. 3.4 +/- 0.05 mg/g in controls, P less than 0.01 for both). Reduction of cardiac weight was associated with increase in both myocardial concentration and content of hydroxyproline in surgically treated rats and in medically treated animals. Ventricular catecholamine concentration was increased after nephrectomy but was unchanged by captopril treatment.