In order to test the additional efficacy of the combination of a beta blocker (penbutolol 40 mg single dose) with molsidomine (2 mg single dose), a double blind cross-over trial was performed in 30 patients with stable angina pectoris. Stress tests were done before and 1 h after the beta blocker alone and the combination therapy. Some training effect could be detected on comparing results from the first and second days. Combined therapy showed a better response of resting systolic arterial pressure, resting and maximal diastolic pressure, heart rate gain (from rest to maximal effort) and particularly in the angina severity score. All of these variables changed significantly in comparison to the beta blocker alone, 46 out of 60 post-drug ergometric studies were negative; of the 14 positive tests, 11 followed the beta blocker and only 3 the combined therapy. The combination of a preload reducer molsidomine and a beta blocker may be adequate for patients only partially compensated or with cardiomegaly and/or a depressed ejection fraction.