Biochemical (myocardial DNA, RNA, and hydroxyproline) and humoral (plasma [PRA] and kidney [KRA] renin activity) factors were determined in spontaneously hypertensive rats (SHR) and normotensive Wistar controls (NR) before and following treatment with minoxidil or propranolol. Minoxidil (150 mg·litre⁻¹ drinking water) effectively controlled blood pressure (17.3 kPa vs 24.9 kPa [130 mmHg vs 187 mmHg], P <0.001) despite marked and sustained increases in both PRA and KRA ventricular weight which were not reduced and myocardial DNA, RNA, and hydroxyproline which were increased by minoxidil (P<0.01). In contrast propranolol did not reduce blood pressure in SHR but ventricular weight was reduced somewhat (3.1 ±0.4 mg·g⁻¹vs 3.4 ± 0.09 mg·g⁻¹, P < 0.05); in both S HR and NR, KRA, and PRA were lowered by pranolol. Methyldopa which controlled blood pressure and lowered PRA led to a reversal of hypertrophy. Thus, although blood pressure control is obviously important for reversing cardiac hypertrophy, it may not be the sole factor for the development and reversal of cardiac hypertrophy.