Fifty-three adult patients suffering from various degrees of essential arterial hypertension, which was not controlled with other antihypertensive drugs, participated in this study with the intention: To demonstrate the effectiveness of a 20 mg or 40 mg daily muzolimine dose as complementary treatment. To determine whether the effective dose obtained can be maintained for a long-term administration. To verify its tolerance. Therefore, muzolimine was administered in addition to the basic treatment, which went on unmodified during this study. A laboratory set of examinations, three controls of systolic and diastolic blood pressures and heart rate--each in supine and standing position--were performed before starting the treatment. At the end of the two initial weeks of treatment with administrations of 20 mg daily muzolimine doses, the diastolic blood pressure normalized at values below 90 mmHg in sixteen patients. These patients continued the muzolimine treatment taking the same dose for seven days, being submitted to two more controls during this time. As the normalization was confirmed, laboratory controls were repeated. Thirteen patients of this group continued the same treatment for three months. The remaining thirty-seven patients, who did not normalize their diastolic blood pressure, immediately started a second treatment period of two weeks, receiving a 40 mg daily muzolimine dose. At the end of this period, diastolic blood pressure normalized in twenty-four patients, decreased significantly in six, moderately in five, and remained unchanged in two. At the end of this second period, laboratory tests were repeated. Nineteen patients of this group continued the same treatment for three months.(ABSTRACT TRUNCATED AT 250 WORDS)