The antihypertensive effect of the preparation celiprolol was studied in a double blind experiment versus acebutolol in 60 patients (30 males and 30 females), with an average age 40 years. Only patients with hypertonic diseases, stage I-II, according to WHO classification were included in the study. The treatment Lasted 4 weeks. The criteria for a good effect were the normalization of the blood pressure and the absence of adverse effects. There was no statistically significant difference between the percentages of the reduced blood pressure, attained by both preparations. By the end of 4th week, 56.7 per cent of the treated with celiprolol were with normalized blood pressure, and 46,7 per cent--with acebutolol. The following adverse effects were observed: light gastrointestinal manifestations, weakness, dizziness, tremor, impotence. In some of the patients those effects were transitory but in 4 patients, treated with acebutolol, the treatment was discontinued because of the adverse effects.