Exercise-induced Q-waves were encountered in four Caucasian males presenting to the Cardiac Clinic, Tygerberg Hospital, with chest pain suggestive of angina pectoris. This phenomenon occurred in four out of a total of 1943 patients undergoing treadmill stress testing (Bruce Protocol) during a two-year period, giving an incidence of 0.21 percent of this ECG response. Two of the four patients (cases 1 and 2) were documented to have coronary atherosclerosis by selective coronary arteriography. One of these patients may well have been experiencing coronary vasospasm. One of the remaining two patients was a teenager whose exercise response was probably normal, whilst the last patient could have had ischemic heart disease (IHD). This most interesting and rare response to exercise (stress) testing is discussed, emphasis being placed on its incidence, mechanism and clinical significance in IHD and other conditions in clinical practice. Awareness of the occasional transient nature of "pathological" Q-waves, whether these occur at rest or during exercise, has an important bearing on such acute therapeutic interventions as intracoronary thrombolysis and percutaneous transluminal coronary angioplasty.