Plasma viscosity, haemoglobin-oxygen affinity and red cell flexibility were determined in 16 patients who had angina pectoris but no objective evidence for spasms or obstructions in the coronary arteries. Reference data were obtained from healthy controls and from a group of patients with angina pectoris and multivessel coronary artery disease. In the non-coronary angina group mean plasma viscosity (+/- SD) was in the normal range (1.3 leads to 0.06 centipoise). The same was true for haemoglobin-oxygen affinity (P50: 25.9 +/- 1.7 mmHg). Both red cell rigidity (71 +/- 20 mmHg) and red cell fragility (142 +/- 95 mg/l) were significantly higher (p les than 0.0025) than in the control group (54 +/- 10 mmHg and 63 +/- 29 mg/l, respectively). The group with coronary artery obstructions did not differ from the controls. Thus rigid red cells appear to be related to the syndrome of angina pectoris despite normal coronary arteries. In the light of previous findings of local perfusion abnormalities in these patients, inflexible erythrocytes could be an additional factor compromising myocardial capillary flow.