Markers suggestive of enhanced free radical (FR) activity have been demonstrated in patients with chest pain and normal coronary angiograms. This may be of pathogenetic importance because FRs impair vascular relaxation and are generated following episodes of myocardial ischaemia/reperfusion. Fifteen patients with angina pectoris, normal coronary angiograms and either a positive exercise tolerance test and/or abnormal dipyridamole thallium tomogram were studied along with 15 age-, sex- and smoking-matched controls. A peripheral venous blood sample was obtained to measure the following FR markers: malondialdehyde, plasma thiols, red blood cell glutathione and superoxide dismutase. No significant differences were detected in the levels of any of the FR markers between either the group of 15 patients with chest pain and normal angiograms or the subgroup with positive exercise tolerance tests when compared to the controls. There is therefore no evidence of enhanced FR activity in patients with chest pain and normal coronary angiograms in peripheral venous blood samples.