In order to minimize muscle noise in the exercise electrocardiogram, Mason and Likar proposed a new lead system where the limb electrodes are instead placed on the trunk. The Mason-Likar system is widely used for both the resting ECG before exercise and recordings during exercise. Several studies have, however, reported great differences between this lead system and the standard lead system. This study shows greater R wave amplitudes in leads II, aVF and III, smaller R wave amplitudes in leads aVL and I and thus a vertical shift of the frontal plane QRS axis for the Mason-Likar system compared with the standard system. For many years another lead system for exercise tests with the bicycle ergometer has been used in our laboratory. The limb electrodes are placed at the proximal part of the arms and the left iliac crest. This lead system yields ECG signals with a low level of muscle noise. The differences between this lead system and the standard ECG are much less pronounced than the differences between the Mason-Likar ECG and standard ECG. We propose our lead system for exercise tests with the bicycle ergometer.