Since our first studies on hypertrophy regression, this parameter has achieved an increasing interest in the treatment of hypertension. During the past 8 years we studied different groups of antihypertensive drugs with the use of magnetic resonance imaging (MRI). This article discusses the antihypertensive drug carvedilol. We examined 17 patients with diastolic blood pressure of at least 95 mm Hg and left ventricular wall thickness of at least 15 mm. Measurements were carried out before and after treatment with 25 mg/day carvedilol for 6 months. We demonstrated a significant regression of septal thickness from 17.7 to 16.3 mm. At each wall, three measurements at different points were performed by MRI and the means were calculated. Left ventricular ejection fraction and wall motion did not show any significant changes in radionuclide ventriculography after treatment. The diastolic blood pressure was reduced from 98.0 to 88.7 mm Hg. All differences are significant (p less than 0.05). There was no significant correlation between the extent of regression of septal hypertrophy and the degree of pretherapeutic hypertrophy, the age of patients, or the dimension of blood pressure reduction.