In a double blind trial the authors studied the effect of beta-adrenoblocking agent Trimepranol (Spofa, Czechoslovakia), in 35 patients with ischaemic heart disease (IHD) associated with angina pectoris, and in another 42 patients they compared the effect of Trimepranol and Obsidan (GDR). The daily doses of Trimepranol and Obsidan averaged 80-100 mg and 160-200 mg respectively. In two thirds of the patients the diagnosis of IHD was confirmed by coronary arteriography. In 46 patients the authors examined the tolerance of physical exercise before and after 3 to 4 weeks of Trimepranol and Obsidan therapy. Trimepranol was effective in 81% and Obsidan in 83% of patients with angina pectoris of effort. The two drugs were distinctly less effective in patients with both effort and resting angina pectoris (54 and 64% respectively). Trimepranol treatment was associated with a higher incidence of side-effects such as bradycardia, arterial pressure decrease and bronchial spasm than Obsidan treatment.