Experimental evidence suggests that free-radical damage and antioxidant defense may play an important role in the pathogenesis of coronary heart disease. We have examined the association between plasmatic glutathione reductase (GR) levels and the prognosis of patients with unstable angina. We have evaluated 37 patients, under the age of 75, diagnosed with unstable angina and 19 healthy volunteers. The patients were divided into two groups: the first group--10 patients with unstable angina with readmission in the following 6 months--and the second group--27 patients with unstable angina and favourable evolution. GR was measured in dynamics during hospitalization period. After discharge, the patients were monitored and the following data were recorded: months of follow-up, death due to cardiovascular cause and onset of major cardiovascular events. In patients with unstable angina there was a statistically significant higher increase of GR on admission to the values of the control group (p < 0.0001). Subsequently, plasmatic levels begin to decline, so that at discharge, the GR is similar to the control group. Plasmatic levels of GR were statistically significantly lower in patients with unstable angina without cardiovascular event than in patients with readmission in the following months (p < 0.05). In conclusion, patients who experienced unstable angina and without cardiovascular events during follow-up had lower GR plasmatic levels and that GR activity was an independent predictor of cardiovascular events during follow-up.